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.