Ben,
In your defaults.cfg:
[Virtual-hosts]
* = "basehost.cfg"
www.benryder.co.uk = "foo.cfg"
benryder.co.uk = "foo.cfg"
Where foo.cfg = your configuration file for www.benryder.co.uk
And no, you won't run out of lines to add virtual hosts in the .cfg file.
~Matthias