my 26 month old daughter was taking her nappy off in bed, so I got her pull ups. If you point out the mickey mouse to him and point out how great they are maybe he will. Seeing himself in something different may work for a while or not at all.
Also have you thought about putting him in a bed, that way he'll get out of bed and hopefully come into your room. Prop a pillow at the side that way he won't fall out.
Who know just a couple of suggestions.
Juanita, SA, 2yr and 5 yr old daughters