Can not change stack order

Hi, this is my first post and first flash project…

I’m doing a simple animated scene involving 3 cups changing positions.
I made each cup a symbol (movie clip) on a separate layer and used motion guides to animate them.
Problem is: I need to change the ?stack order? during the animation so that cup_2 passes “behind” cup_3 and then cup_2 passes “in front” of cup_3.
Cup_2 passes behind ok because it is in a layer that is below cup_3. But how do I make cup_2 then pass in front of cup_3 which is in its own separate layer that is listed below the layer of cup_3 ?

I have done a lot of searching and tried a number of things like:
_root.Cup_3.swapDepths (_root.Cup_2);

but to no avail
I’m using MX Pro 2004 and the file in question can be found at:
http://www.siteofhand.com.au/_media/SiteOfHand_logo.fla

any help on this would be great…