D.P.
That's weird b/c I always thought they didn't actually poop while they were sleeping. Before he falls asleep maybe? After my son went to bed, I always checked him before I went to bed and if there was a smell.....I really mastered the art of changing him without waking him up! I just couldn't stand the thought of him sleeping in a poopie diaper, I guess. I'll bet you could try that. Good luck. Otherwise, I'd just change his sheets very frequently.