What about lying in the lounge room watching a movie with him? I know its not ideal, but as he is way too young to stop the day time sleeps, maybe just sitting and resting might do - least its something! At least he is 'resting' for some part of the day. SOmetimes thats just as good as a sleep. You wonder where they get there energy from dont you? My #1 DD stopped her daytime sleeps at 23 months. I was heartbroken, as i knew it was too early. Like you said, my DD#1 is a good night sleeper, in at 645pm. right thru to 8am some nights.
Good luck