nginx userdir + php-fpm

default

server {
    listen       80;
    server_name  localhost;

    # ... other default site stuff, document root, etc. ...

    location ~ ^/~(?<userdir_user>.+?)(?<userdir_uri>/.*)?$ {
        alias   /home/chroot/home/$userdir_user/public_html$userdir_uri;
        index   index.html index.htm index.php;
        autoindex on;

        include php5_generic;
    }
}

php5_generic

location ~ \.php$ {
    include         fastcgi_params;
    fastcgi_param   SCRIPT_FILENAME     $request_filename;
    fastcgi_pass    unix:/var/run/php5-fpm.sock;
    fastcgi_index   index.php;
}

Debian 7.
This works for a chrooted user, which home is in /home/chroot. Look at the line number 8 in default file above.
php5_generic is in /etc/nginx/ : all the location of included files are relative to the default nginx configuration file folder (/etc/nginx in debian).