Okay, so he is slow and lazy just doing flatwork and then he rushes at the jumps? Why are you using a crop over the jumps if he rushes them? He may be trying to escape the crop, realizing that it's coming and trying to jump as quick as he can so he dosen't get hit? If that isn't the problem, I would just try the circling method. Ride in a straight line to a jump, make it obvious that you are going to jump-when you feel him start to speed up (like he is going to rush it) then quickly circle away (without jumping) and try it again until he remains calm while jumping.

And yes, please don't pull the reins over the jump-that might cause him to start refusing. And I would rather be on a horse that rushes than refuses .

A different bit while jumping may be in order. I would look at something not harsher, but something that gets his attention.