I have a friend at a trim shop who places a small washer over the end of the tip on the back and uses a real small counter-sunk oval head screw that he taps into the hole of the snap with a hammer. Otherwise, some other options are to use roll tip punches. Neither of these will look right, but from the outside will be fine. Only way to make it look right is to get the NPD tool or buy a rivet squeezer.