Robert,
It would be difficult (if not outright impossible) to coordinate between a Couch managed template and a non-Couch managed script.
The best way, IMHO, is for you to go ahead and convert the list.php into a Couch managed template.
You are right, this will change its canonical URL but that does not mean you'll lose the existing PR - URLs of pages keep changing in due course of their life-times. That is why we have the '301 Moved Permanently' directive.
You can place it in your .htaccess file so that visitors accessing the older URL get redirected to new address and your PR simply gets transferred to the new page.
Hope this helps.
It would be difficult (if not outright impossible) to coordinate between a Couch managed template and a non-Couch managed script.
The best way, IMHO, is for you to go ahead and convert the list.php into a Couch managed template.
You are right, this will change its canonical URL but that does not mean you'll lose the existing PR - URLs of pages keep changing in due course of their life-times. That is why we have the '301 Moved Permanently' directive.
You can place it in your .htaccess file so that visitors accessing the older URL get redirected to new address and your PR simply gets transferred to the new page.
Hope this helps.