Hi, I was solving the same problem. Finally I got through it this way:
Go to edit aircraft, then find aileron servos, elevator servos and rudder servos on the left. Set the values as desired - in case of setting the airplane "more 3Dlike " set the +values larger, - values smaller . Save the plane modification as " 3D" for example. You can choose it when loading airplane from modification bar. I know, it is not proper dual rates solution, but it works for me.
Cheers,