This took me a while to figure out and i'm not sure the way I do it is the best way but it works. First your aileron servos have to be in separate inputs in the receiver; aileron and
Aux 1. Than in the DX7 go in to the setup mode (holding the down and select buttons when turning it on) and under wing type select falperon on. Now under the normal menu (pressing down and select with the transmitter on), go to flap system. You will see norm, mid and land. These correspond to the flap mix switch on the top left. 0 (zero) is norm, 1 is mid and 2 is land. Select 1 on the flap mix switch and than move the carrot (select button) to the mid selection and increase or decrease the % to set the amount of flap for that switch position. than select flap mix 2 and do the same for land. I use 50% and 75%. Now on the right of the display you will see elev. This allows you to trim the elevator with that flap setting. Most planes will pitch up with flaps so I set some nose down, maybe like 15 for flaps one and 20 for flaps two. Make sure the elevator actually goes down when you do this, if something is reversed it might display DN but the elevator goes up. At the bottom you will see AUTO. this will automatically retract the flaps at a set throttle setting. I use between 50 and 75%. This is for a missed approach, if you punch the throttle up, the flaps retract. Last of all (and this took me a while to figure out) if you are all trimmed up in normal flight and you throw out the flaps and she wants to roll, retract the flaps, land and use the Travel Adjust to limit how far the right or left aileron extends with that flap setting. If you use the trim or sub trim, it will affect flight with flaps up. Using travel adjust does not affect the ailerons when they are retracted but limits how far each one extends. In the travel adjust menu their is aileron and flap. If the plane rolls right when flaps are extended, increase the travel of the servo on the right or decrease the travel of the servo on the left. depending on weather its in aileron or aux will determine weather aileron of flap controls it. It takes a while to get it trimmed for pitch and roll but once its done you will slow faster and be able to fly slower. The last thing I do is on the aileron rudder mix menu, set the bottom line to SW: FLAP2 and the RATE to something like 30%. This automatically gives you rudder with the aileron when you are in the flaps 2 setting. It helps turning at slow speeds and coordinate the turning.
The other thing is practice setting this stuff up at a rather slow speed and good height. Be ready to retract the flaps if it pitches or rolls. Good luck and let me know if it works. Its been a while since I've configured this thing, but I think I got everything.

Mark