At school, they have these fabic thingies stuck inside the doorway, infront of the hole the metal part of the lock goes into. Basically, because of the placement, it makes it practically impossible to card because there is no space to slide the card in.
It's kind of hard to explain (And I'm terrible at explaining to begin with), but basically see if you can stick something in the doorjam between where you would card and the metal-thingy that's being carded (My termenology is great, ain't it?), while still allowing the door to close.
If you still have no idea, I'll try to swipe a Digital Camera and take a picture to show you what I mean. Picture's worth 1000 words, after all.
On a side note, I know it's Student Rez, but you might want to talk to whoever owns the place and try to convince them to get better locks.*shrug* An idea
Good luck
EDIT - Got a Picture
See where the black circles are? The Fabric thingys are stuck there.
Good luck again