Mike is away for a bit. I'll try and help.

The Eclipse has several mixes available to manually program as you desire. BUT there are default mixes and these may serve your needs. Activate a mix, adjust the variables and use two servos with their respective connectors into the listed RX ports, and the servos will work as one. This method is preferred over a wye. You are able to center and adjust the surface end-points as needed.

As mentioned below, the single problem I note for your application is the mix MUST be activated by a switch, this switch must be left in the ON position...