I recently found myself having to make some php configuration changes which are specific to a particular subdomain on my Mediatemple DV web host, and found that yet another part of subdomain setup is mildly broken out-of-the-box. This is the sort of thing that most people who need it can probably figure out for themselves, but I'm posting the solution hoping someone will find it useful.
On my DV the domain specific apache configuration is located in /var/www/vhosts/domain-name/conf/, where domain-name is of course replaced by your actual domain name. In this directory you should find at least httpd.include, and possibly vhost.conf as well. If you open httpd.include you'll find the following alarming warning at the top: