Communicating through a scroll window component

Awhile ago I got some great help when I needed a method to communicate from the (linked) content in a scroll window component to a dynamically attached mc in front of the scroll window. The code was pretty simple!

calendarPagesBtn_mc.onRelease = function(){
    _level0.slideHolder_mc.attachMovie("calendarPages", "calendarPages", _level0.slideHolder_mc.getNextHighestDepth());

And I’ve been using it quite a lot, as we create a lot of scrolling timelines with clickable callouts.

However now I need to be able to communicate from the attached mc BACK to the linked content of the scroll window. I’ve tried a few things and nothing’s working yet.

Any help would be appreciated!

EDIT: All I need to do I think is check if the mc in front of the scroll window is empty, but my mind is a blank right now.