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It seems to me that there is nothing preventing Eucharistic adoration from fulfilling the obligation of penance.
Let's have a look at the document that regulates the Friday obligation in the United States: the 1966 Pastoral Statement on Penance and Abstinence. It remarks on the history of the Friday abstinence from meat and explains why it may not be appropriate in the modern age as the best way to unite ourselves with Christ's passion. For example, in paragraph 20, the bishops say
Accordingly, since the spirit of penance primarily suggests that we discipline ourselves in that which we enjoy most, to many in our day abstinence from meat no longer implies penance, while renunciation of other things would be more penitential.
They go on to say that the obligation is altered in the following way (22 and 23):
Friday itself remains a special day of penitential observance throughout the year, a time when those who seek perfection will be mindful of their personal sins and the sins of mankind which they are called upon to help expiate in union with Christ Crucified.
Friday should be in each week something of what Lent is in the entire year. For this reason we urge all to prepare for that weekly Easter that comes with each Sunday by freely making of every Friday a day of self-denial and mortification in prayerful remembrance of the passion of Jesus Christ.
Finally, in urging people not to criticize others for not abstaining from meat, they say (paragraph 26)
We should warn those who decide to keep the Friday abstinence for reasons of personal piety and special love that they must not pass judgment on those who elect to substitute other penitential observances. Friday, please God, will acquire among us other forms of penitential witness which may become as much a part of the devout way of life in the future as Friday abstinence from meat.
So the key points are that it should preserve a sense of penitential witness, that it should be elected by the individual, that it should be an act of self-denial and mortification, that it should be a prayerful remembrance of Christ's passion, and that people should not pass judgment on people who observe the Friday penance in ways that differ from their own.
I would argue that Eucharistic adoration would be a worthy way to follow these observances, as long as they fulfill the individual requirements. It should be a free devotional act, so there are unlikely to be a strict list of options.
In the document Holy Communion and Worship of the Eucharist Outside Mass (PDF), we can see the following about Eucharistic adoration (Supplementary Appendix, paragraph 3):
Eucharistic devotion fosters a deeper participation in the paschal mystery. The faithful are more closely associated with the grace of salvation effected by Christ in his death and resurrection.
This seems to me very much to fulfill the requirement of "remembrance of Christ's passion", and if it fulfills the other criteria, it is satisfactory.