Universal Subscription Mechanism from Randy Charles Morin. Yep, this is more like it.
Inserts an <atom:link> element into the feed pointing to the source URI. Depends on the server responding with the mime type "application/rss+xml". He suggests discouraging the use of "application/rdf+xml" - I'm not sure that is necessary (or desirable).
PS. nearly missed this - he's also done some code implementing the client side, see this blog post.