You can also use a Smart-Fly servo combiner("Equalizer II") for the elevator halves from one receiver jack. I prefer these to mixing from the Tx. They are easy to get right and matched. Ihave used these to match two servos to a rudder (both push/pull with rod linkage)and they are able to completely eliminate binding of the two servos on one control surface.

http://www.smart-fly.com/products/Eq.../equalizer.htm