I built the SS 60 last winter and did exactly what you want to do. I would not modify the ailerons size at all, but it is easy to install dual aileron servo's in the wing.

There are several methods for mounting the ailerons out in each wing panel. The method I used on my SS was to just build a couple mounting rails out in each wing panel just behind the main spar. Then mounted the servo so just the servo horn will extend beyond the depth of the ribs. When covering, you just cover around the servo arm. This is a simple and effective method. BTW - I used a couple of small balsa pieces around the servo to serve as something for the covering to stick to.