My daughter is 3 1/2 as well and I know she would probably love to give up naptime, but that just isn't an option in my house
I explain it to her that we all just need our quiet sleep/play/reflection time each day so both the kids go down for naps and I can catch up on homework, housework, or even take a little nappy myself. I don't care if she sleeps, but she does have to go into her room for some quiet time. Often she just reads some books or plays for about 45 minutes and on days that she is actually tired she will fall asleep for a bit. Would it be possible to require some quiet reflection time?
Or else, i am all for cuddling up in bed and watching a kids movie with a lock on teh door so he can't get out
Trap him in so you can doze!!
Is he a super active kid who won't slow down at all? If I put on Toy Story for my daughter and give her something to eat and something to drink.... I could probably sleep through the whole thing and I don't think she would move until the movie ended. My son on the other hand.....