i dont know how much space you have, but if you hold the lock so the loop part is point upwards, wack the part thats sticking out where you put the key in.
Code:
------
| |
| | |- wack here
| | v
============ <--- key hole
also you can try
http://www.wikihow.com/Break-a-U-Lock
did it break the casing around the lock, or bend the U shape and allow it to pop out?
leverage techniques will be tried after a short effort with a bic pen