joe wotton

Hi I wonder if anyone can help me,I have a Sanwa sd10 g radio,and have just purchased a BJ craft Fantasista 170 pattern plane that has what they call a nose thruster wich basically is a rudder at the front of the model working with the conventional rear rudder,the problem is that I cant get the front rudder servo to operate as a slave from the master rudder,because when I select rudder as master, the only aux channel it will allow me to use is aux 4 but when using the normal 2 aileron tx setup aux 4 becomes the flap channel so the slave only works in one direction.
I have tried re allocating the channels but then both servos work together and I cannot adjust throw or reverse independent channels.
Can anyone suggest how this can be done? any help would be very wecome.
Regards Joe