I don't know if it would be at all posible, but I was looking through mods and hacks for Vbulletin and I saw a hack that implements an anti-proxy system. Where by disallowing any users that connect through a proxy. I don't remember the details about how it works, but I remember that it wouldn't affect alot of people or something. LOL I don't know. Vbulletin isn't open source, so I don't know about this hack. The link to it is http://www.vbulletin.org/forum/showthread.php?t=68590&highlight=anti-proxy. I think it'd be a great thing to have to deter abusers.

Ha, so I'm not entirely crazy. This was pretty much what I was looking for http://www.ranking.ws/index.php/articles/simple-php-proxy-blocker. Now I'm just wondering about it's incorporation into an XOOPS block or something of that nature.