Not sure if you can do this on the DX7 but my DX9 I can actually do a mix of switches, I can take a 2 Position switch and mix it too a 3 position switch so I can get 6 positions or to any other switch ., slider or rotary knob.
If you can mix 2 2 position switches that would give 3 position for your flaps, flip switch first 2 position would give % of flaps then 2nd 2 postion switch would give another 2 position % of flaps.