New video games? Special trips? Food? You might try this approach and give him the offer of first 1 then 3, then 5 nights in a row going to sleep in his own bed gets a special treat. Then be totally cool if he doesn't make it. "Okay, we'll just put this new video game up here in the closet until you can go to sleep in your own bed for X nights in a row".

Might not work, but I've seen it work for others. Just a thought.