Those keys are basically macros mapped keys. You can program multiple key strokes all into one stroke. I think the OP is talking about the "G" keys. If I'm wrong then never mind.
Yeah, same as mapping wheel buttons to keys in the Logitech (or any similar software). You map a button to the 'K' key, go in game and assign it by pressing that mapped-button and it shows as 'K'. Having the G13 keys show up as their own keys is what the OP was hoping for in rF2, since rF1 doesn't support it.
