Using the throttle trim to adjust the elevator brake compensation, like the Futaba FF9
Using a global variable

A high channel is used; Throttle trim to channel 10

A curve is used to set the amounts, make the curve steeper to increase trim steps, 
these setting give 38% to 24% brake compensation for maximum and min throttle trim

Channel 10 is used as the value as GV3, as in CF12

Channel 2 is the elevator and gets its value from the throttle and weight from GV3, switch SA arms the brakes 

A curve is used to correct non linear compensation

The brake compensation can now be adjusted with the throttle trim, adjust curve 3 to get even brake compensation

You may need to reverse the curve to suit servo direction: