Also making sure that his head is tucked in and he's on the bit will help him from falling apart before jumps it will make him have to lift his legs. Cavaleties would work good too start off with at least 6 and then add more when he gets comfortable
I'd do Cavaletti's then do a 2 stride the a jump it helped my boy
When my friend's horse was knocking everything and just didn't seem to care about the jump, she rode with either a dressage whip on both sides or just her dominant side and over the jump she would tap her hoer horse's front foreleg.
I do use wooden poles. He's fine jumping under 2'9 but once we go higher he doesn't put the effort in to pick up his feet. Do you think Bounce jumps will help?
I agree with jasmine (although it won't actually hurt your horse, just come as a surprise as it will send a bit more of a shock through the leg).
Your horse may also be a bit on the forehand or not sitting up enough. Try halfhalting more on your way to the jump so they aren't at all strung out and have the contained energy to take off with more power.
Have you used wooden poles? Sometimes those work if your horse hits it, itll hurt a little causing them to pick his feet up more :) or maybe asking for a big stride before so they really push off :)