Don't know if it will work with a USB numpad, but there's a freeware program called Sharpkeys that I use on my laptop to make the Capslock key into a Windows key. It might do what you're looking for.

You arrive home and toss your car keys on a table near your front door. It's an ordinary habit that is all today's thieves need to launch a "relay attack" to capture the signal from your key fob, ...