It is possible but I don't know if the DX6 could do it.

YOu could do it on two switches:

1) Wings in and out
2) Ailerons go from low rate, zero when closed, to high rate - 100% response when open.

You would have to remember to flip them both and to time them right so the ailerons did not come on before the wings opened.

The alternative would be to mix the switches together so that when you flip the switch both things happen at the same time. There might be a timing issue as you would activate ailerons before the wings came out. So you might need some kind of delay device that would delay the ailerons from activating if they would be blocked when the wings were swept back.

Could create some control problems as the plane would change its controls mid flight. That could be very tricky to manage.