 <p>You could have him use a dynamic DNS service like dyndns.com or no-ip.com. That way he can setup a domain name like someguy.dyndns.com which would always resolve to his ip (he'll probably need to install a small daemon/service/program to automatically update the IP though). Then you can add a rule into your .htaccess like <code>allow from someguy.dyndns.com</code>.</p>