I'm not sure I understand what you mean by "from the Aggregate side", but it sounds like you want the media URLs for each submission?
The API that Briefcase uses is documented here. You first have to get the list of submissions, then get each submission, then in that response, you can find the downloadUrl for the media files.
You could also use the JSON publisher and have a listener/server that grabs the links from each submission. I don't love this option because if the listener is down, then you miss a submission.
You could also consider tweaking Briefcase's command line mode to write the links instead of the image files.