I've seen two other NextStars with this problem, and the best solution for these was to install dual aileron servos. The wing has the pockets ready to accept standard size servos, and there are pull strings installed at the factory in each wing panel to pull the extensions through. I won't have access to my NextStar until Jan, but can get some detailed pictures of the installation when I get back home (I installed dual servos for functioning flapperons). I also set the differential throw through radio programming.

Hogflyer