WP MU installation question

I am trying to configure WP MU to use subdomains instead of sub-directories. Now based on WP instructions, I shall edit the httpd.conf file and add the line:

ServerAlias *.example.com

But as I can see from our CentOS box, there is only one httpd.conf on the server and this file is responsible for the whole box, now since I don’t want to change the configuration for ‘all domains’ hosted on this server, I was wondering isn’t there a way where I can make this change ‘only’ for the domain responsible for our network?

Thanks in advance for your time and efforts