Configure driving keys

Hey
I've got GP4 and I've installed the latest patch 9.6 on it.
Now I've tried to change the driving keys, only once I realized how to do it (i pressed middle mouse and then it let me click on "Change driving keys".. but it doesnt work for me again, don't know why)... that's nice, but i'm used to shift gears with left and right "alt", and i tried to configure that, but the game won't get ALTs but anyother key...
I've been looking everywhere for a solution, so I have to ask this here: How can I choose the ALTs?
Maybe there's a mod for the game that gets it or something.

Thanks