I don't think the underground man can come to Christ, at least not as things stand, because I think he is actively participating in the unforgivable sin--that is, a refusal to ask for forgiveness, to turn to God, to humble himself, to repent, to have the courage to be who God wants to make him into. To blaspheme the Holy Ghost is not to denounce him, but to ignore him, to act as though he doesn't exist. Now the underground man is a psychological masochist, he takes pleasure from his own inadequacy and sickness and repulsiveness. He's not palyzed into inaction, he actively chooses it (though he might deny that), he actively chooses to move from idea to idea, activity to activity, because that is what makes him happy.
He says at one point that he wish he could be a lazy man, because at least that would be a positive description of him, at least that would be something. But he is something. He is the man that Jn. 3:19-21 speaks of: "And this is the condemnation, that the light has come into the world, and men loved darkness rather than light, because their deeds were evil. For everyone practicing evil hates the light and does not come to the light, lest his deeds should be exposed. But he who does the truth comes to the light, that his deeds may be clearly seen, that they have been done in God."
Darkness doesn't always have to be overt sin. Sometimes it is that, yes, but more often it is a state of mind. Out of the heart of man comes a thousand horrors. And this is not a man who is merely psychologically trapped in a crappy situation, the way some spousal abuse victims become trapped. This goes far beyond that. And until and unless the underground man is willing to change that, then God can't and won't force him to change for the better. God already gives him the motivation and opportunity to change (Phil. 2:13), but the underground man ignores the call.