I teach design in a college department that includes several courses in product design. The wide variety of techniques we use to create prototypes of various products the students design has given me a few ideas on how one might create their own tactile buttons as a screen overlay.

Cast them. You'll need a simple negative form. Easily create negative buttons by drilling positive holes with a flat bottomed drill bit. You'll need a casting resin, but it could be sylicon gel or something similar you might find at a craft shop or hardware store. Whatever you use, be sure to coat the mold with a release agent... something the resin won't stick to. I've used spray PAM (vegetable oil) occasionally with good results. Soap might work too.

You can make indivudual buttons, and stick them onto your flat screen protector. You could make a whole array of buttons, already cast in place, with the screen protector applied over then buttons as they hardened in the mold.

Another thing you might try is to find some clear stick-on "feet" often sold at hardware stores and intended to be put on speakers and other hard objects to prevent them from sliding around or marring your shelves. Perhaps Radio Shack would be the place to look. I've seen square and round "feet", and in varuous sizes. They are already adhesive, and might be just the ticket.

I've got more ideas, if anyone is interested.

Dave