I saw this article yesterday which gives some novel ways to deal with trolls .
I particularly like the idea of 'hellbanning' - trolls aren't blocked from the site, but their posts are made invisible to everyone but themselves. So there they are, starting threads, posting inflammatory replies etc and gradually starting to wonder why everyone is ignoring them. Eventually even the thickest, most persistent troll would give up. A very effective way of enforcing 'don't feed the troll'.
Worth a try, MNHQ?