Yeah I don't think the G keys have a corresponding console command ID. You could use the Logitech keystroke organizer to set a G-key to press "y" and then "Hi" and then "enter," that's sort of a workaround.
The G11 and G15 recognize the G keys as F keys. You might have to program them in through the logitech software. I've had trouble doing this and gave up pretty quick