You could seal the hinge line using some extra covering. Ive never done this yet, but a lot of folks at the field do this to help reduce airflow into the hinge gap.

Essentially you would cut yourself a strip of covering material, fold the hinge as far down as it will go (not attached to servo at this point), and iron on the covering. The flip the wing so you have access to the other side and do the same. Wa-la, hinge gap sealed.