You can't.
(Well, you could write something similar to the Shift+G toggle)

Yeah, i got everything working on the F11 side (Post if you want em), and im working on a Shift+H toggle for gears now...

Um, how do i change shifting via scripts? ie "Shift = Shifter" but i dont know how to do it!

/shifter shifter
/shifter sequential (rebind shift_up and shift_down accordingly)

You can read all that in the Commands.txt

Thanks! couldn't find it in Commands.txt, myself

erm, is everyone elses Rev 101, as mine seems to be different to everyone elses (ie the shifter feels great, the brake pedals is soft etc)