To keep things simple for this smaller EDF, Y the Ailerons and have the tail planes as Stabilators or Pitch only by Y off the elevator channel (one servo has to be reversed).

Tailerons: You could get a SM2 mixer or Vtail mixer ( http://www.dionysusdesign.com/produc...roducts_id/174 ) and Y off the aileron channel to the mixer and connect the Elevator channel to the other side of the mixer to drive the two tail servos as Tailerons Ptich and Roll.
With the other side of the Aileron Channel Y'd you can drive the ailerons.
If you want to get creative, Select Flapperon as wing type, which will make the aileron channel and the Flap channel to drive your Ailerons/Flapperons.
Still with the External mixer, have the elevator on one side and use on the other side... I don't remember if the DX7 allows you to slave channels from the initial setup. If it does slave the Aileron to the Gear channel. If the DX7 cant slave then just mix the Ail to the Gear channel and connect the gear channel to the other side of the mixer.
In this setup you have both Ailerons on the wings, Flapperons, can mix Elevator to flap for tighter turns, while also having the tailerons also helping with your roll rate since the tailerons are both Roll and Pitch.
When you extend the flapperons, the tailerons still have sufficient roll control.

Just make certain you setup your taileron servo linkage so that the linkage is in the inner most hole of the servo arm and on the outside or one in on the horn. This will make it much less twitchy and allow you full travel of the servo for the range required in the tailerons.

If you setup flapperons, you must have tailerons otherwise you will not have enough roll control from the flapperons alone.

Flapperons or flaps are fine and they Do Not cause a stall; the pilot does.
Flapperons have more area and create more lift and drag. In most aircraft it also adds a pitch moment that needs to be compensated by both Pitch and thrust. Because many RC jet pilots do not use a Stabilized approach that they were originally supposed to have learned (see AV Web http://www.avweb.com/news/leadingedg..._199047-1.html) turns into the bad habit of trying to glide in like they are the space shuttle. What catches them is with flapperons, the aircraft slows down very quick because they are not approaching under controlled power. Especially if you get gusty headwinds that suddenly slows the ground speed futher, but th airspeed then is increased causing the model to climb and then the gust stops. This leads to the pilot either then trying to power on or they pitch up and down to contol the altitude and it drops because of insufficient airspeed. They then declear that it was the flapperons that caused the stall. That's just pilot error.