To use AUX4 for nose steering just use one of the mix functions.
1) Get rid of the Matchbox
2) Plug the rudder servo into the RUD and steering servo into AUX4
3) Inhibit AUX4 on the DEVICE SELECT screen
4) On the WING TYPE screen do not mate it to Rudder. Set the Rudder mate to inhibit.
5) Use one of the Program mixes: MIX3 - MIX6. Mix RUD>AUX4. Select the GEAR Switch to activate. Set the gear up positions to
0% and the gear down positions to what ever rate you need for proper steering.
6) If you want to use a gyro for steering just plug it in to AUX4 and plug the steering servo into the gyro.

The above works. I have a couple of my jets set up this way.

Joe