WOW knows mouse button 4/5 and any key on the keyboard, but the extra keys on keypads (Nostro, X-keys, G15), are pretty much you program them to do stuff. The best/safest way is to pick a key combination you never use (CTRL-ALT-A/Z) and program them as that key. It is safest, since you only generate one keypress that is broadcastable and you can then map macros/hotbars to those keys and get results. One keypress, one action. I won't even talk about that those keypads can do macros, cause that can lead to problems, just use one weird key combination and map a hotbar/macro in the game.

Extra info. I have 2 Macs and I can't seem to get ALT to pass easily. So I use Numpad 0-9 and CTRL-Numpad 0-9. I also use a VNC (virtual screen) to get my PC broadcaster (HKN) to talk to the Macs. So just cause something isn't designed to do stuff, doesn't mean it can't be done, just takes time, patience and inginuitiy (spelling) to make it happen. Don't give up if it is something you want. Especially if it works right, you might set a new trend for others to follow. (Saying intimidate is WAY better than using one key that one char uses that has to be passed and no one else can use---so I would love if a voice commands work).