It is actually possible. My SSC planes weight in just under 2.5lbs, so I tape on some lead on the CG to make weight.

However, I've also found that my SSC wings are too slow for A class, so I while I do use the same fuse, I swap wings betweent the two classes. Same root chord and same airfoil, just smaller span for A.

Oh, and A and SSC really aren't directly related. It's better to think of them as seperate classes, even though they share the same engine dispalcement.