According to Roman Catholicism, can the death penalty for heresy be squared with any New Testament teaching?

The sin of spreading heresy (and not merely assenting to heresy) is a species of scandal, because it leads the faithful into error regarding the faith. Scandal generally can be considered to be a capital crime, because it has the general effect of destoying souls. Christ had this to say about those who cause scandal, or, in other words, cause others to stumble:

At that time the disciples came to Jesus and asked, “Who, then, is the greatest in the kingdom of heaven?” 2 He called a little child to him, and placed the child among them. 3 And he said: “Truly I tell you, unless you change and become like little children, you will never enter the kingdom of heaven. 4 Therefore, whoever takes the lowly position of this child is the greatest in the kingdom of heaven. 5 And whoever welcomes one such child in my name welcomes me. 6 “If anyone causes one of these little ones—those who believe in me—to stumble, it would be better for them to have a large millstone hung around their neck and to be drowned in the depths of the sea. 7 Woe to the world because of the things that cause people to stumble! Such things must come, but woe to the person through whom they come! 8 If your hand or your foot causes you to stumble, cut it off and throw it away. It is better for you to enter life maimed or crippled than to have two hands or two feet and be thrown into eternal fire. 9 And if your eye causes you to stumble, gouge it out and throw it away. It is better for you to enter life with one eye than to have two eyes and be thrown into the fire of hell. (Matt 18:1-9, NIV)

We are very familiar with this passage, and I fear that may cause us to gloss over it, and to not really consider what our Lord is saying here. First, He says to the disciples that they will only enter the Kingdom if they become like little children. That is, believers are to be childlike in their faith. He continues: if you cause one of these little ones - who believes in me - to stumble, you should be put to death (by drowning). These little ones is not in reference to literal children, but to the faithful generally, who He has just said are called to be like little children.

He continues on, hyperbolically stating that you should destroy even your own body parts if they would cause you to stumble. These eyes and hands are allegorical - they refer to the members of Christ' Body who cause the innocent, child-like faithful to stumble. One of these sort are the heretics. They are to be cut off and thrown into the fire. That is, they are to be destroyed.

Now, we also ought to pray for their repentance, and try to help them to repent. As a good physician knows, if he can heal the ailment in a limb, he ought to prefer that cure to amputation. But, there may come a time when the limb is gangrenous and utterly corrupt, and it must be amputated for the good of the whole body.

St. Thomas Aquinas uses this same analogy of an ill body when he writes of capital punishment generally:

we observe that if the health of the whole body demands the excision of a member, through its being decayed or infectious to the other members, it will be both praiseworthy and advantageous to have it cut away. Now every individual person is compared to the whole community, as part to whole. Therefore if a man be dangerous and infectious to the community, on account of some sin, it is praiseworthy and advantageous that he be killed in order to safeguard the common good, since "a little leaven corrupteth the whole lump" (1 Corinthians 5:6). (ST II-II Q64 A2 co)

So if a heretic is infectious to the body, it may, in certain situations, be necessary to put him to death, in order to protect the whole body. Better that the body would enter maimed into paradise than to be thrust whole into Hades.