Allow CNAME records to connect to point to my server?

[anagio]

Our web app gives each user a sub-domain. I'd like to offer some larger
plans CNAME's so they can point one of their own domain names with a
CNAME to their sub-domain on our server 

ie; username.ourwebapp.com

customersdomain.com => CNAME username.ourwebapp.com

Our NGINX server is configured with wild card sub-domains, but uses a
perl conf to read valid sub-domains from a file. If the sub-domain
doesn't exist they get a 404.

So I am guess to allow users to create CNAME's to their sub-domain on
our server we will need to create a name based virtual host and a new
config file in sites-available include their subdomain on our server, as
well as an alias of the customers own domain? Is that how it should be
done or is there another way?

Thanks

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,219463,219463#msg-219463