Along with a spoofer if you plan on smoking again in the dorms (which by the way is a bad idea in itself) at least be more cautious. Use a fan system to get the smell out of your room. If you are unsure how to do this and can't figure it out from a friend I suppose reply back. Before you smoke in the future make sure to hold a lighter up to the crack on your door. If it doesn't get blown out (in the direction of the window not the direction of the door) your room needs a fan system/better draft.

I don't know how the ventilation system in the dorms where you go work, but at least in my experience the dorm rooms had a tendency to recycle the air through underneath the door and through the crack and literally pull it out into the hallway.