If there isn't enough room to mount the servo arm on the other side, you will have to buy a reversing Y harness. They are quite expensive and have an adjuster so that the servos are matched.

If you use a different channel for each and couple them together in the transmitter, be careful that the trim works on both channels. In a Hitec transmitter (and probably others too) the trim will only work on channel 2, the original elevator channel, and not on, say channel 7 or whatever channel you use for the other elevator half.

-David C.