if the seat is sculpted, i bet he could hack out the whole 3/4in or even more(just small flat spots in the bottom- and many whole seats are hard) and just put the glue or velcro on the foam thick parts, say near the edges so you can get to them if probs.
test out first, if too much out, glue in a 1/8 sheet from below or press in some 1/8 neoprene from above.
but the thigh braces are too personal to predict.