Hi Shaun,
I know how you feel since I had similar moments in my projects and in many cases you see the solution when you look at the problem from different perspective. You just have to keep trying
I don't know how your project looks but I'm guessing that you have one mediator for Flex application instance and no matter how deeply your list component can be nested you always know when you need to display that data (Flex has many events for view components states) and you can always be sure that this list component is on display tree.
The way I would try to solve this problem is to dispatch custom event from the list component and let it bubble up to the application instance, in application mediator listen to this event and fire notification that will trigger command for registering mediator and proxy as in Cliff example for standard version of PureMVC. This should be very simple solution, one event and one notification.
I hope this helps you
Miroslav