Showjumping - Jump Off Turns...?

Does anyone have any advice or more specifically, exercises (flat work or jumping) that will improve my jump off turns and really help my horse get his hindquarters underneath him when he turns. Please only answer if you are experienced/knowledgeable... i'm not a novice but am just looking for some exercises or pointers. Iv notice while watching the FEI World Cup qualifiers that the horses that turn the best are the ones that turn using their hindquarters and not the ones that run a bit on the forehand or drop their shoulder...