Oh I LOve to play jokes.
Might try this one. Get a long string or rope of some kind and tie it to the outside of the bedroom door. And then tie the other side of the string/ rope to another door across the hall. Have the bedroom door closed and the another door open somewhat. So when he goes to open the bedroom door the other door will slam and he won't be able to get out of the bedroom without help. Did this to a coworker, and I used lighted christmas lights. Was funny, she laughed till she needed depends on. Good Luck and Happy Joking to you. Monty