activating ch 5 to activate 2nd servo on ch3

Guys dont shoot the noob all at once, but here is what I am wanting to do:

I have a devo 7e transmitter, I have a model where ch3 is used for left and right, however what im wanting to do is set the transmitter to operate a second servo on ch3 but only once i have activated the fmod switch - can someone help as I am going nutty trying to fathom it

Any assistance you can offer would be great

in which port are the two servos on your RX? 3+5?
And which Stick on the TX are you willing to use? Aileron?

If so, goto Model setup
switch to advanced Mixer
Goto Mixer page Channel 5 and switch from Simple to Complex
Select AIL in the SRC field and choose switch "Flightmode1"

Hope this helps...i`m on Devo6/12

oh you little beauty cheers pal - im an old school flyer and not used to all this digital milarky yet