nginx - userdir with user permissions

What I want to do is have the usual server running user files like this:

http://users.example.com/~user1/stuff.php

which would be stored somewhere in /home/user1/www or something like that, but running with that user's permissions. So, scripts in the /home/user1/www directory can't access files/folders in the /home/user2/www directory (unless UNIX permissons permit it).

I read a solution using vhosts and a new pool for each vhost, but for hundreds of users that's probably to heavie. Is there any workaround?

Note that I'm running nginx in a Raspberry Pi, so this is just a home project, nothing really serious.