g1smd - 9:49 am on May 19, 2011 (gmt 0)

The canonical tag can help you.

You can also tell Google to ignore certain parameters when found in a URL.

If /page1 resolves to a PHP script, you could have a few lines at the beginning that do your "recognise the visitor" bit (and maybe set a cookie) and then issues a 301 redirect to the canonical URL.