Roger,
I was able to do what you wanted by setting up two Pmixes. The first one is flap-flap, set at 100% in both directions. The second mix was flap-aileron, set at -100% in both directions. Both mixes were set to switch H in the Up position. Now when the switch is Up the servos works as ailerons but you can move VRA anywhere and they won't act as flaps. Move the switch down and the servos will go wherever VRA is telling them to go. Don't forget to activate Flap-Trim and set it at 100% or whatever total amount of flap travel you need. Hope this helps.