After wrestling with cushioned unmounted stamp foam backing with "cling" for several years I found Mount-It Glue at Club Scrap for a little more than the cost of a single sheet of that other technique. You just brush it on and let it dry.
glue box. It's so easy to make one and all you need is a bottle of the Mount-It Glue and a never-had-pizza-in-it pizza box. Most pizza places will sell one to you for a low cost; some will even give you one.
You spread a little glue over the top and bottom of the inside of the pizza box and wait for it to turn transparent. Put the cut pieces of the unmounted stamps face down in the box. This holds them in place while you spread the glue on the back of the stamps.
When the glue is transparent, I like to check the edges and rub off any glue that is on the sides of the stamp. Then they are good to go. Best of all, no cutting through foam sheets that coat my scissors, even my teflon scissors, with goo and no dangerous encounters with scissors afterwards trying to clean off the foam sheet glue goo lol. If this was a black and white TV commercial, this is where I'd hold up the glue and say, "Mount-It, the Safety Stamp Mounting System" with one of those teeth sparkling smiles lol.