Wouldn't the "random number in a query parameter" be a persistent user
id ?
The only think i can think of, that would be truly non-persistent-id ,
would be to use some sort of redirect or cookie...
1- All links to subscribe / read go to "rss:a"
2- If "rss:a" sees a non-unique cookie "seen=1", it redirects to
"rss:b" / or displays the content
3- if it doesn't see the cookie, it sets one... logs it... then does
the redirect/display
I'm not sure how rss cookies work... it seems like some use systems
describe HTTP cookies , others use url-encoded strings
If the privacy policy allows it, the method you thought of would
probably be ideal. If not, I'd push for a privacy policy change --
you should be able to persist a random identifier , like any of the
analytics suites out there do. i believe that's what feedburner and
feedblitz do too