Actually, I've been told that you can connect up any five servos and that the Cortex will figure out the functions during setup. Say you had a jet that used only Ailevators (no Ailerons), you could connect the 2 Ailevator servos and if you had dual rudder servos, you could connect each of them to the Cortex separately and still have a channel to spare. As long as your transmitter was setup to provide the correct inputs to each channel during setup, the Cortex is supposed to be able to figure out how to stabilize a plane that uses these types of functions.

Of course if you had separate Ailerons, Elevators and Dual Rudders, you would need to tie the dual rudders together somehow. Personally, I would be inclined to use a matchbox rather than a Y harness to allow me to fine tune each rudder servos travel, centering, etc.