i'm an upholsterer & i modify my seats trying to get the perfect fit all the time. Just mark the seat foam with a pen then use an electric knife to carefully cut it out, this works best when you are a short arse`like me as the seat hight will drop by about 2 inches. Do it carefully then just use 800 grit sand paper to get the final shape the way you want it. I will talk you through it if you like. Mr. Woo.