I was chatting to a luthier who was using them, he said he hasnt had a finish scratching problem yet, apparently designed not to harm the finish at all, i will try them on one of my poocasters i experiment on throw it around on them a bit, they are only a few $$ if the dont work out.

They are based on the painters pyramid, that dont mark the surface.

Heres the blurb on them
Rockler Bench CookieŽ Finishing Cones lift your project off your bench with minimal surface contact, keeping it stable during the entire finishing process! Custom sized to fit snugly over the incredibly popular Rockler Bench CookieŽ