The answer is:

Set up your own proxy on a high port.

My guess is that this school's filtering system isn't very advanced. Probably just a proxy server w/ a firewall to block certian types of outgoing traffic. and the traffic they block is probably all through port number. It is possible to block traffic at the packet level by it's header but I know they aren't doing that. My guess is if you set up a proxy on a high port like 65500 it will be unfiltered. If it is, I would check to see what other services besides http, port 80, that they allow out. place your proxy on this port and you will be all set.