All sorted!
1. Select wing type = flaperon. Inhibit flap switch.
2. Plug right aileron into RX aileron (ch2) Plug left aileron into RX Aux1 (flap channel)
The radio automatically mixes the two channels and gives them a common trim. As the flap switch is disabled therefore radio assumes no flaps they work in unison.
Spent two hours fiddling with 4 sets of mechanical linkages for ailerons to get them neutral. Aileron Trim works on all four wings. Last job - rebind to get failsafe positions. :woohoo: