If you have access to his dorm room, drop/hide things like deli sliced meat behind desks, under the bed, etc. It will take a few days to take effect, so he won't immediately suspect you, and the smell will linger even after he finds and removes them.
Place craigslist ads for casual encounters with his phone # in different craigslists around the state.
Call his professors and other friends (either make it a private call, use a relay service, skype, etc) and just repeatedly say his name. They will start to loathe him on principle for it.
Another thing we did to someone this semester that was kind of fun is telling professors and other people it's his birthday. Repeatedly. People usually start getting into the prank and will join in. It's juvenile, but if he has a short fuse, hilarity will ensue every time he hears "happy birthday!"
Sign him up for all sorts of junk mail. If you can fill his mailbox daily, his RA (or whatever you call your residence hall advisers) will start to get pissed off at him.
