W.C.
Operating on the principle that if you physically exhaust him, he will be so tired he won't wake up, I have these suggestions:
You might consider shortening or eliminating his nap time. He is about that age.
Another thing is to increase his activity level. Swimming lessons at the Y are really good for exhausting him, as are regular outings like long walks without the stroller everyday (I sound like a dog walker!! :) ) or playing games outside with Daddy everyday.