I have built a few different freestyle seats and my latest one seems to work the best.
Take your stock seat apart, cut a piece of plywood the size of the top of the seat, add a bit of thin padding on top. Cut the foam leaving a 3-4 inch wide piece up the center. Lay the ply on top of the stock seat foam. Then hook the plywood to seat base so it cant pull up (we used a bunch of duct tape), then recover the seat and cut the grab areas out. Finished job looks clean, adds a little height and is still plush for hard landings.
I will have to get better pics, it works awesome tho.

Oh and heres our white trash makeshift wood seat haha! My buddy was throwin huge seat grabs with this sketchy piece of garbage.