Quick one: target to combobox in dynamically created movieclip?

programming flash
1

I have a movie clip “input_mc” from the Library and attach it to the main timeline using this.attachMovie(). It contains comboboxes, and from the main timeline I want to control the comboboxes, like addItem(). How do I do this?

From the main timeline:
this.input_mc.comboboxInstanceName.addItem(“foo”) - doesn’t work
input_mc.comboboxInstanceName.addItem(“foo”) - doesn’t work
_root.input_mc.comboboxInstanceName.addItem(“foo”) - doesn’t work

I’m puzzled…there must be something really easy that I’m missing…

Thanks!!!