It turns out that you can use moreover.com itself to aggregate, filter, and remove redundency from a category of news and then get an RSS feed of the results. 

First, go to the moreover.com categories page.  Select a category or do a search.  Somewhere in the URL that lists the results, you'll see an o=portal.  Change it to o=rss and subscribe to that feed.  (Thanks to Amphetadesk). 

Still, I'd like to be able to do it myself.