You used to be able to buy something like this at Pearl or other craft centers. It comes in sheets you heat in water in the microwave and shape to fit. My mom had a set of screwdrivers with custom grips. I think it was called thermal decorative plastic.
this appears to be some sort of silicone compound vacuum packed with a softening agent that evaporates in ~30min and finishes in 24hrs. So don't need to heat prior to use, and probably a bit more flexible once cured