Okay, here's an easier fix. A pin vise, a 5/64" dia. drill bit, a #4 flat head wood screw x 1/2" long, and a Phillips screwdriver is all you need.
Here is an extra O-31 MTH left-hand switch I have. Carefully hand-drill hole, screw in the flat head screw until it is flush with the top of the rails, and you're done. The screw should take up enough gap to allow the roller to cross the rails without getting hung up.
CAUTION! I don't think there is any internal wiring at the spot I drilled the hole, and I don't think I hit any wiring on this switch. Hence the hand-drilled hole with the pin-vise. Proceed with extreme care if you go this route, so you don't mess up any potential internal wiring!