Do your best to make him a jump shooter from the perimeter. Frye did a decent job of keeping Aldridge off the block, and a good job contesting Aldridge's shots when on the block. HOWEVER, much of this is likely Aldridge not having the smarts/heart to fully exploit the defensive tactic. I figure Duncan will. However, I still believe the best defense against Duncan will be a swarming zone when in with the ball in the post, a fronting-technique when attempting to get position in the post, and instant doubles if Duncan tries to do anything with the ball besides shoot while on the perimeter.
Or, they can go -for-tat and play him straight up the way SA used to defend Amare. Make Duncan himself beat you and do your best to defend/disallow the others from getting shots, specifically open threes.