I'm guessing if it's been going on a while then the 30 min naps are because he has a build up of OT.
I would suggest if the am nap is short you try a much shorter second A time (as he's probably completely OT already by the second nap), so the day would look something like:
6am wake
9.30-10 nap
12.30/1pm nap and hope for a long one!
Really EBT if both naps are short. Or 6.30 if the second nap is good.
What do you think? Can you ever resettle a short nap?