PRO HOP using the KEYBOARD

Does anyone know how to do Pro-HOP using the keyboard? What is the name of the key in the .kfg file?

You have to press one of the crossover buttons for 1-2 secs.

I have these lines in my kfg file:
bind K_F RXAXISCHANGE
bind K_C RYAXISCHANGE

So it's F, C or D (standard crossover).