Window to window to Flash communication

Hi folks.

I have been tasked with the following:

From an external browser window/tab, be able to send data **to ** a SWF residing in another browswer window/tab. This could also mean having the external container communicate to the wrapping container which in turn tells the SWF what to do.

I am currently able to use ExternalInterface to communicate between the SWF and the wrapping HTML container, but how does one communicate from a non-wrapping HTML container?

Most of my searches are examples of launching data from the SWF to a popup window which is not what i want.