D.S.
Definitely let him play/talk to himself for a while! He'll let you know when he's really ready to get out. This is a great time for him to learn and try out new words and sounds.
I did this for my son and I think it's led to him being OK with being in his crib when he's not tired. If I put him down for a nap and he doesn't want to sleep, he'll lay there and quietly play or talk to himself.
It's also a good time to secretly video tape him and get some of that early babbling recorded for posterity!