I have only played one sax that I thought needed a riser and that was only the D. it was an early WWBW 'The Woodwind' tenor. but since it was not for me, I didn't do anything. I mean, I had to contort my hand to get the D - never had to do anything like that before. And of course, I never have used risers on any of my horns. If I had to do it I probably would use cork but hard rubber would be good. You can get fake 'pearl' plastic in slabs and that might be best.