I am running a site that is available via many domains. So all domains depend on the same code, but depending on the requested domain, the correct information is shown to the user. In Plesk, I have one domain set up and it has domain aliases for all the others. This works ok.

Now, I'd like to be able to use subdomains on those aliased domains. Like the domains, the subdomains will be used as input for the system to display the correct information. So, they are not a fixed set.

What I have done:
- In DNS I have added *.example.com CNAME example.com to the main domain. This is automatically copied by Plesk to all the aliases. So DNS-wise, I think it's ok.
- I have added a vhost.conf file to the main domain, containing ServerAlias *.maindomain.tld.

This works for the main domain. But still, not for the aliased domains. And there is no place to put vhost.conf files for the aliased domains.. How do I tell the server to respond to those domain's subdomains as well?