I've been studying up on making my own kydex/leather holster. Granted, I haven't made one yet, still looking for dense enough foam. From what I've seen it's all been with toaster oven and heat gun. Your referring to what you would use to press the kydex into the trigger housing, I'm guessing? Use a heat gun to apply local heat to your kydex, then clamp it back in the foam boards.