[CentOS] RedHat to CentOS transition

I installed RHEL ES 4.0 on a new server because I had the disks. The problem is that the new server does not have a RedHat network subscription and can't use Up2date to keep itself current. We set up a script that just runs apt once a week, but I am curious whether there is some way of changing the box into a CentOS machine and using your Up2Date to get updates from one of the mirrors.

I read on the White Box site that they use a Fedora Yum package and a modified version of Up2Date to accomplish the same thing as RedHat's tool. I assume CentOS is the same way. Can I just install those packages and modify the /etc/redhat-release or is there more to it?