First, I'm fairly certain your Spektrum Radio is NOT the proper set-up for this use. This radio is designed for "Park Flyers" which are flown "close in". The radio may not have the range needed for R/C sailplanes, which among all R/C vehicles are operated at the farthest distances between the transmitter and receiver. Per the HORIZON Hobby Electric Flight Catalog for this spring, aircraft using this radio should not be flown much farther then 3/8ths of a mile from the transmitter. I'm not familier enough with this system to completely rule out it's use. Maybe someone with more knowledge about it can help.

It sounds like the sailplane you have, is designed for two aileron servos and two flap servos. Y-harnesses should be used to combine the aileron servos and another used to combine the flap servos. Plug the Flap Y-harness into the Auxiliary channel and the aileron Y-harness into the aileron channel and you should be able to do what your asking.