AS2 drag and drop a masked content from loadMovie clip

In the main content, when I have a movie clip like this   a1.a2.a3 while  a3 inside a2 and a2 inside a1, and a2 is a masked layer movie clip.

I can drag and drop the masked content (while a1 stay still) with like this   a1.a2.onPress = function () { startDrag(this); }  and a1.a2.onRelease = function () { stopDrag(); }

but then what i need is a1 stay in main content, while moved a2.a3 to an external .swf, and use loadMovie to put .swf(a2.a3) back into a1, and I can still drag/drop a2.a3 when a1 stay still.

I tried differetn methods they all not working.  I've learned that you need to create another MC inside a1 like this a1.a4.a2.a3 ( while a2.a3 from loadMovie clip). it only work if I want to drag a1. but if I want to drag masked content a2.a3 it still doesn't.

I really need help it's a project for work.