I can't build you a cup, but the other night on TV I was watching a program that had to do with a family that makes prosthetics. They had a clear plastic material that they just stuck in a hot water bath for a few minutes, brought it out and fomred it over a persons stump and worked it in and made aperfect duplicate in clear plastic of the stump. Then it hit me, when I had surgery on my left arm the physical therapost made me a hot water formed plastic brace affair. I went and dug it out and tried to solvent weld it with Weldon #, 4 and 16 and it worked beautifully. So if you can find a source for this type of plastic there is no doubt in my mind that one could not fashion a mold from various items stuck together with hotglue just to get the shape and then mold this plastic down around it all just fine.. The plastic my brace was made from is better than 1/8" thick and just playing with this stuff over and over has opened up a laot of new ideas for things I could make with it. Sort of like vacu forming without the need of a special oven and vac machine....Just hot water and your hands.
My physical therapist also had flesh, black, gray, white and clear pieces in her cabinet now that I think about it.....gonna have to give her a call and find the name and manufacturer of that stuff......