many ways,, but since you have the 14c Rx I'd build a programmable mix

go to the prog mix screen, they are pre set but you can modify any of them
make CH2 (ele) master, what ever channel you pick slave

Settings

Rate +100 up and down
offset 0%
Mix "on"
Trim "on"
Link "on"
SW (Doesn't matter)
Posi- Null (sets the mix on always, no switch controls the mix)

Go to the AUX-CH screen and set that channel switch or knob as "Null" there too,, that way nothing will move that servo but the "master" CH2

Now go set your reversing, sub trims and end points for each

good luck