After doing some chores, I spent 10 minutes and made a test sample with a leather punch, a rubber furniture pad and a adhesive dot just to see if the concept was workable. The button actually stands up a little too high, I could use a piece of thinner material, maybe even leather. The adhesive dots I happened to have were 1/2 in diameter, and I used the punch to cut them to the same size as my button.
The photo was taken with my 5D MK II and the test button. It seems to stick pretty well, I'll play with it and try making one thinner.
Update, I tried to peal it off, but the flimsy rubber pulled apart instead, so I'll find some more durable rubber or leather. At least the adhesive is stronger than the material.
I think I could stamp out these for well under 5 cents each.