The syntax looks like this:
http://api.flickr.com/services/feeds/photoset.gne?set=<photoset_id>&nsid=<user_id>
For example:
http://api.flickr.com/services/feeds/photoset.gne?set=72157640206531056&nsid=7155605@N03
To find out a user’s flickr ID got to:
http://idgettr.com/