Adding it to the banlist doesn't quite work. Peerguardian should work, however (although I haven't tested it). This will also block ahat from joining your server, but as far as I'm concerned that's an added bonus.

This program is completely idiotic in the way it is being used. While I can see potential good uses for it, right now it's just a piece of annoying crap. I fully endorse putting a stop to it by any means possible.

Edit: Seems this guy has a dynamic IP. Perhaps just blocking the entire IP range for newfoundland (I believe that's where he lives) will suffice.