In order to keep the host that is originally defined in the main httpd.conf alive, you have to define a VirtualHost with the same values for it first. (see http://httpd.apache.org/docs/2.0/vhosts/name-based.html - Main Host Goes Away box )
I'm feeling too lazy to write something that parses the original httpd.conf right now and creates it automatically, sorry. But perhaps worth mentioning in the README