With a GWS (or similar) V-tail-Elevon mixer you can plug both elevator servos into the mixer outputs.
One of the mixer inputs is plugged into channel 2 on your receiver for elevator.
The other mixer input must also be plugged into the receiver.. for this example I use channel 6 which is unused in this application..
Both elevator servos will then trim identically from the trim button, and respond to dual-rate changes and EPA adjustments.
.
But a Y-harness accomplishes the same thing.