This is a really interesting question. I just tried playing with it for a bit, and I was able to approximate this for a fair number of emails (and with a large helping of kludgyness) by sorting the search results by subject which puts no subject emails at the top.

Of course within that pile is down to scanning.

I see why it's tricky since the search is indexed, but it does feel like there might be a way.

Have you tried asking their helpdesk?