Well, technically you kinda could, but I'm not sure how accurate it would be:
Set up the page as frames (2 frames, top takes 100% of window, bottom takes 0% (trust me)). The 0% frame's source could be an script set to refresh on a timed basis (meta-refresh) say every 10 seconds or so passing some unique user_id that you ingeniously put on it, and, upon receivng this ID, stores it into a database table.
Now, if you wanted to see who was viewing this page, a query to this table would include records where the view_date is within 10 secs of the query date.
when the user breaks outta the page(leaves the framed document) voila!
Kinda dorky and stupid, but I think it work (God only knows why you want to know this).