What are some techniques to practice Anatta with the five aggregates?

The method you described is correct.

Acknowledge that the ear hurts, and observe how this pain originates, changes and ceases, in a detached way.

“Bhikkhus, when the instructed noble disciple is contacted by a painful feeling, he does not sorrow, grieve, or lament; he does not weep beating his breast and become distraught. He feels one feeling—a bodily one, not a mental one. Suppose they were to strike a man with a dart, but they would not strike him immediately afterwards with a second dart, so that the man would feel a feeling caused by one dart only. So too, when the instructed noble disciple is contacted by a painful feeling … he feels one feeling—a bodily one, not a mental one.

“Being contacted by that same painful feeling, he harbours no aversion towards it. Since he harbours no aversion towards painful feeling, the underlying tendency to aversion towards painful feeling does not lie behind this. Being contacted by painful feeling, he does not seek delight in sensual pleasure. For what reason? Because the instructed noble disciple knows of an escape from painful feeling other than sensual pleasure. Since he does not seek delight in sensual pleasure, the underlying tendency to lust for pleasant feeling does not lie behind this. He understands as it really is the origin and the passing away, the gratification, the danger, and the escape in the case of these feelings. Since he understands these things, the underlying tendency to ignorance in regard to neither-painful-nor-pleasant feeling does not lie behind this.

“If he feels a pleasant feeling, he feels it detached. If he feels a painful feeling, he feels it detached. If he feels a neither-painful-nor-pleasant feeling, he feels it detached. This, bhikkhus, is called a noble disciple who is detached from birth, aging, and death; who is detached from sorrow, lamentation, pain, displeasure, and despair; who is detached from suffering, I say.
SN 36.6

Thinking 'there's an ear, and it hurts' rather than thinking "my ear hurts" is a proper method. Similarly, viewing anger & fear as merely elements of anger & fear will make them go away & make the mind calm again.

Regarding the primary question asked, the suttas contain the stock phrase:

Yadaniccaṁ taṁ dukkhaṁ;

What is impermanent is unsatisfactory.

yaṁ dukkhaṁ tadanattā;

What is unsatisfactory is not-self.

Thus, the Anatta-Lakkhana Sutta begins the wisdom inquiry with impermanence. The Buddha asks:

• Now, that which is impermanent, is it unsatisfactory or satisfactory?
• Now, that which is impermanent, unsatisfactory, subject to change, is it proper to regard that as: 'This is mine, this I am, this is my self'?

Therefore, here, impermanence takes a significant focus. Once impermanence is clearly discerned, it is plainly obvious that which is impermanent, subject to change by the forces of nature; subject to change beyond our control; that which also cannot be relied on for lasting happiness; certainly cannot be regarded as "This is mine" because what is impermanent can be subject to change & loss anytime.

The five aggregates are like "borrowed goods". The five aggregates do not belong to anyone. The five aggregates are just creations of nature. Therefore, the suttas contain such phrases as:

Nāyaṁ, bhikkhave, kāyo tumhākaṁ napi aññesaṁ

Mendicants, this group (kaya; of aggregates) doesn’t belong to you or to anyone else.

SN 12.37

Therefore, bhikkhus, whatever is not yours, abandon it; when you have abandoned it, that will lead to your welfare and happiness for a long time. What is it that is not yours? Material form is not yours. Abandon it. When you have abandoned it, that will lead to your welfare and happiness for a long time. Feeling is not yours. Abandon it. When you have abandoned it, that will lead to your welfare and happiness for a long time. Perception is not yours. Abandon it. When you have abandoned it, that will lead to your welfare and happiness for a long time. Formations are not yours. Abandon them. When you have abandoned them, that will lead to your welfare and happiness for a long time. Consciousness is not yours. Abandon it. When you have abandoned it, that will lead to your welfare and happiness for a long time.

MN 22; also SN 35.101 regarding the six sense spheres

While direct estrangement (nibbindati), i.e., seeing the five aggregates as 'alien' (parato), can certainly occur when the five aggregates are clearly seen with a clear mind as being merely aggregates & elements (dhatu), suttas such as the Anatta-Lakkhana Sutta and Sīlavantasutta include impermanence & unsatisfactoriness because this is a natural gradual way to feel estrangement. The Sīlavantasutta says:

Sīlavatāvuso, koṭṭhika, bhikkhunā pañcupādānakkhandhā aniccato dukkhato rogato gaṇḍato sallato aghato ābādhato parato palokato suññato anattato yoniso manasi kātabbā.

Venerable Koṭṭhita, a virtuous monk is to wisely pay attention to the five components of attachment as impermanent, unsatisfactory, disease, cancer, stabbing, misfortune, affliction, alien, disintegrating, empty and impersonal.

For example, in AN 3.39, when young Gotama realized he would be subject to aging, illness & death, he lost the pride (mada) associated with his youth. This is an example of estrangement arising primarily from realizing impermanence & unsatisfactoriness; which naturally reduced the pride of self in young Gotama.

Or MN 54, as summarised in MN 22, goes into detail about why sensual pleasures provide little gratification, much suffering and despair, and that the danger in them is still more. When clearly seeing the unsatisfactoriness of sensual pleasures, which is related to their impermanence unable to sustain lasting happiness, an estrangement from sensual pleasures occurs. MN 22 summarises:

The Blessed One has stated that sensual pleasures provide little gratification, much suffering and despair, and that the danger in them is still more. With the simile of the skeleton…with the simile of the piece of meat…with the simile of the grass torch…with the simile of the pit of coals…with the simile of the dream…with the simile of the borrowed goods…with the simile of fruits on a tree…with the simile of the butcher’s knife and block…with the simile of the sword stake…with the simile of the snake’s head, the Blessed One has stated that sensual pleasures provide little gratification, much suffering and despair, and that the danger in them is still more.

MN 22

Therefore, in conclusion, the Dhamma shows it is not only the perception of non-self (anatta) that generates estrangement (nibbindati). The perceptions of impermanence & unsatisfactoriness also significantly contribute.

Yes, the best way to anatta is serenity. Intellectual understanding does not help at all. It can help you remove noise from your life, but the real understanding comes from serenity.

When you are absolutely calm, you become an observer automatically. The second link of dependent origination is the real deal. You have to stop doing anything. This is not just for a few hours. You have to stop any kind of fabrication for days and at some point, mind becomes observer and it doesn't want to do anything because of the deep peace the mind experiences. And then it is revealed that everything keeps on going automatically as if we are watching a movie.

It feels as if we were forced to become an observer by the universe until our death. But, peace has this quality that sucks you in and you become estranged to the skandhas automatically.

Wisdom can help but wisdom without peace is useless. Serenity is the real deal which helps us experience whatever the Buddha says first hand.

I think this is just going extreme because these things(ear getting hurt, etc) will keep happening as long as the body exists. Physical pain is best to be avoided.

What the Buddha teaches is to just relax. The main teaching of the Buddha which is the Anapanasati sutta, is just depicting the relaxation after we have cut off enough of the background noises. If you have relaxed enough anatta and all the rest of it will be revealed automatically. The epitome of relaxation is nibbana.

The big skill in life is to just relax and chill. Buddha would have won Guinness world records or the Olympics in relaxation 😀.

The ultimate technique is to not do anything, just sit like a log of wood for days. Awakening is guaranteed but most people cannot even go 10 minutes without touching their phone or PC.