Unless you get a wildcard SSL certificate (can you say EXPENSIVE?), then your proposal of using the subdomain will not work. When you get a cert, you have to specify if you want it for
www.example.com, or just example.com, or maybe secure.example.com. Once you specify the correct FQDN, you cannot then just use it for yyyy.example.com, without throwing up SSL errors.
The point is... even if you could devise a way for it to function like you want, the SSL cert would still throw up errors because the FQDN doesn't match what your ordered the cert for.
- Scott