HELP : How to setup FF8 with a 4CH RX

Hi,

Have a small handlaunch glider for 3 servos (2 ailerons and 1 elevator). I would like to use my FF8 with a small 4 channel Robbe RX. Choosing the AILERON DIFFERANTIAL mode it means I have to use CH1 and 7 on my RX. But is their a way to disable eg. the throttle stick and to mix CH7 to eg CH3? In other words: would like to use a 4CH RX to operate the 2 ailerons.

Thanks a lot for your help,

Ragards,