The trolls are driving me crazy; I'd like to experiment with a secret ban.

http://www.codinghorror.com/blog/2011/06/suspension-ban-or-hellban.html

A hellbanned user is invisible to all other users, but crucially, not himself. From their perspective, they are participating normally in the community but nobody ever responds to them. They can no longer disrupt the community because they are effectively a ghost. It's a clever way of enforcing the "don't feed the troll" rule in the community. When nothing they post ever gets a response, a hellbanned user is likely to get bored or frustrated and leave.

It looks like there's no way to do this out-of-the-box with phpbb. Is there a way to hack it in?