Speed brake / rudder mixing for flying wing

Thanks ahead of time

I have an rvjet with px4 and the old endurance package plus frsky radio/x8r rx and noticed the large adverse yaw and wang at low speed and also want speed brakes. The way I figured I can remedy this is by using two servos, one per wing, that operate two controll surfaces each and create drag (like duckerons, but not part of the roll system, only yaw and speed brakes). I want the pixhawk to counter yaw using these two channels and to deploy speed brakes too. Is this doable? If so how do I set the two channels to more the servos for these two functions?

Much thanks again!