Set a feed to only show to keep the latest X entries unread

I would like to be able to set a max number of notifications for specific pages.

On my list, some feeds, by their very nature, update much more frequently. Things like major news outlets, large networks or feeds maintained by communities (example: produce much more content than smaller channels. The trainer does a good enough job, but sadly some feeds simply do not use resources like tags or other metadata. I generally keep those in separate categories, but it would be great if I could keep my categories more “natural”.

What I mean is that, using the reddit example above, I don’t need to know every single new entry while I was away. Just the, say, 10 or 15 latest entries are good enough. So, I would go to those larger feeds and set them specifically to keep only the latest 10 or 15 entries as unread. This would keep them more manageable in the same categories as smaller feeds, which I know I want to check all unread entries while I was away. The same applies to some news outlets , which I follow with a firefox extension so they don’t overwhelm newsblur when I use the “All site stories” mode.