Why not Sullinger on the post up? He's doing the dirty work on the glass, let him have some fun on the block.
I think Diaw is one of the better post defenders Sully has played against lately. Very strong, low center of gravity, tough to move, quick feet, hard to get around. Around the same size as Sully.
I'd like to see Sully get some post ups but I think they'll be easier opportunities to work that into the offense on other nights.