Help!!!!!!!!!!!

I am setting up a plane for a friend. I am a JR user. He has the 6XA.

The problem:
He has dual elevator servos. I have been able to get the mix working. I am having a problem getting rid of the other channel. I don't want him to flip a switch and crash the plane. He's been out of the hobby for a while and just getting back in. He gave up trying to program and wants me to try. I need to know how to disable the switch or inputs of either channel 5 or 6. On the JR radios you can go into the ATV of the slave channel and zero it out. It will disable the slave channel input while letting the master mix continue. I tried to do the same thing with the Futaba and the ATV affects both the slave channel and the mix from the master channel.

I've been through the manual twice and can't seem to find the answer.

Thanks