Drag Question - hit area

I remember seeing a tutorial on this but I can’t seem to find it.

I have a draggable mc within a movie clip. I’m wondering how to code it so that when dragged it will move the parent, but I don’t want the parent to be able to be clicked on anywhere…just the one movieclip.

layout: _root.cont_mc.box_mc

if i use:
cont_mc.box_mc.onMouseDown = function(){
this.startDrag();
}

the box_mc will move anywhere i want - good enough.

if i use:
cont_mc.box_mc.onMouseDown = function(){
this._parent.startDrag();
}

the whole thing moves as expected, but the hit area is the whole clip since i’m attaching the startDrag() to that clip.

So how do I move cont_mc by only dragging box_mc?

Thanks.