When you use FMA Co-Pilot CPD4 on a plane with 2 servos on wing (one for airelon) usually you must connect an Y cable to use correctly CPD4 stabilization.
With this configuration you cant use the flaperon mix (it move the 2 wing servo to the same direction to simulate flap).

My idea is to use a V-Tail hardware mixer (it cost under 10$) to use flaperons.

This is the connection schema:

The V-Tail mixer output will be connected to servos, the ELEVATOR input is our flap, i suggest to connect to gear channel, the RUDDER input is the airelon input, you must connect to airelon output of CPD4.

Check on the trasmitter that on gear switch off all 2 airelon are on neutral posizition, then set the position on the gear switch on.

I hope that my explanation is clear.