SonnetCelestial, does this abuser's ip address fall within a certain range? If it does you can ban that entire subnet for a while and then release the ban after a month or two. Shouldn't affect any of your other users unless you are capturing lots and lots of traffic.
Another way, which might actually piss him off more than anything else, is put in a small if/then statement in the login section. Dont' ban the guy yet. When he logs in, have it open up 10 browser windows and 5 of them full-screen, which he won't be able to close unless he knows about "alt-F4". Yeah I learned that one from all those porno sites I used to visit back when I used to have an xxx website myself.
Btw, the later suggestion is not recommended actually. All it does is add fuel to the fire. I just had to post it because it's fun sometimes to dream about revenge...
Oh... one last thing. Try this one... Don't ban him yet. Capture a significant amount of his ip logins and posts, then report them all to his isp all at once. That will more likely get his account canned than if you simply capture a couple of ip sessions and report only those.