Looking for Organization Model for ui Classes

I am looking for a model to organize my ui classes so that more than one class can apply to the same displayObject. Consider this example:

I have a AlphaButton Class extending from MovieClip that changes the alpha state on MOUSE_OVER and MOUSE_OUT.

I have a ScrollButton Class extending from MovieClip that holds actions to scroll a scrollbar.

I want to keep these 2 classes separate so that they may be reusable in other projects. But right now, I want a ScrollButton that has the AlphaButton interactivity.

I can’t attach both these classes to the same MovieClip via the flash library unless one extends the other (which defeats the whole purpose of keeping them modular). Does anyone have a solution for this?