Proportional control of additional T200 (or similar)


I’m in the need to controll one or two PWM outputs, for example servo 9+10 (AUX 1 and two on Pixhawk 1) proportional to controll an additional T200 motor.

I was hoping to be able to assign buttons LT and RT on Xbox controller to servo_1_min/max but I can’t find any way to use buttons LT and RT.
Is it possible to use LT and RT in some way?

Is there any other good idéas on how I could proportional control PWM output on AUX 1 and 2 or alternatively directly control Main 7 and 8?