Depending on the type of doors you have in your house, do the old penny lock. It really only works on inward-opening doors, though.
Here's how: While his door is shut and he is preferably asleep, push in on his door like you're trying to open it but do not turn the handle. Put a stack of pennies between the door and the door jam. It has to be TIGHT. Bring a hammer and couple extra pennies to really get them in there. When he tries to leave his room, he'll be stuck inside. If you do it right, he won't be able to leave, except thru the window.
We used to do this to dorm rooms in my hall frosh year in college, and people would have to call the RA to let them out of thier rooms.
OR
Put a pile of baby powder onto a sheet of paper. Slide it quietly under his door. Slide a straw under the door, and blow thru that thing like you've never blown before. His room will have a light dusting of baby powder all over everything. This can be combined with the penny lock, too. Just to piss him off when he realizes he's stuck in his room, AND there's a cloud of baby powder.
OR
TIDAL WAVE!!! This also only works on inward-opening doors. Partially fill a garbage can with water and lean it against his door. When he opens his door, all that water gushes into his room. It's a f-ing MESS, so be prepared for him to be mad as hell.