Here is your answer. The XPO can solve your problems (product I developed). You need to find a RX for the XF421 to drop into the airplane. Having the second RX on board will completely separate the transmitter programing of the two pilots (master and secondary). So not only will you have full programming available (expo, dual rates, etc) for both pilots, your fifth channel issues currently plaguing you are just not existent with the XPO.

However, you will have to assign a dedicated channel on you master receiver to be responsible for the switching of control back and forth. The XPO allows up to 6 channels to be toggled between the master and the secondary pilot. If your X9303 receiver has 7 channels, then you will pick a channel to perform the control switching and the rest can be shared with the secondary pilot. If your X9303 RX has more than 7 channels then you have even more options (channel-wise) to pick from to assign as the switching channel....any dial or toggle on your X9303 can be set as your new trainer toggle.

Let me make sure I am clear, the dedicated channel on the master RX controlling the switching always remains with the master pilot.

The XPO Co-Pilot ("Wireless Buddy Box") will give you the freedom you want....and no more student stepping on the cord either....

For me to further personalize your answer I would need to know the receiver you are using for your X9303. Please ask me more if something is unclear or you have other points to discuss.