Projects like this are interesting.

A friend took a .40 sized trainer with a flat bottom wing and hot wired some foam to transform the wing to a symetric airfoil. He simply taped the slices of foam to the underside of the existing wing. The plane flew fantastic afterwards. I don't think he had to remount the wing or adjust angle of attack.

In the case of this Q-Tee, I would add 4 inches of span to each wing panel and see what happens. Little wing extenders could be made very light and simply stuck on the existing wing tips with 2 sided tape and packing tape for testing.