something like this?
location ~ \.(php)$ {
fastcgi_pass php_fpm_backend;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME
/usr/share/phpmyadmin/$fastcgi_script_name;
...
}
this catches all files with .php extension.
Posted at Nginx Forum: http://forum.nginx.org/read.php?2,188514,188556#msg-188556