@dudleydes got it to work!
I added input_toggle_fast_forward_btn = "7"
but not to the retroarch.cfg 's
I added it to
/opt/retropie/configs/all/retroarch-joypads
then the .cfg for the joypad, which is " Mad Catz Xbox 360 Controller.cfg "
now right trigger works as FF when combined with hot key for all libtretro systems.
thanks for the help