One of the ways we sell to our customers is that they sponsor page X, and then their banners will show up on pages linked from X. We do all of the logic for this server-side, and the URL never changes. We're moving to a system for counting banner stats that is based on page views from Google Analytics. Essentially, we'll be determining the number of page views for today, seeing what ads were available for those pages, and then dividing.
My question is, how would you calculate the number of pages that were viewed after coming from page X? I'd really prefer not changing the URL in any way, and these pages don't currently use anything in the querystring, and I'd like to keep it that way.
EDIT: It's not traditional banner impressions. Let's say they want to sponsor a page. In our CMS, we set it up so that their ad displays on that page (they become the only company to show ads on that page). We also then force ads on the next page to display as theirs (normally, these ads would be from the random pool).