have a look at this code. with this you can at least use the numpad. im not sure how to get the keyname for it to make it rebindable if that is what you want to achieve.
If it's still unanswered in a few days, try asking the developer, because is is an interesting question. However, not ever pc has a numpad, many laptops do not.
I just need the arrow keys ... but all of them at once I'll give that code a try -
But this was supposed to be a quick fix for my other problem... looks like this isn't good either since I hadn't considered that the numpad is only on some keybpards...
btw, the key_5 doesn't work on numpad. without the above code (which I have yet to try)