[CentOS] Keeping a complete CentOS mirror

Is there a way I can keep a complete mirror of old/new releases of
CentOS 4/5 automagically? In other words I would pull the old files from
the vault site when needed, and new files from one of the other mirrors.
I've seen/used a few scripts but rsync just stomps the old releases with
the latest. The key issue here is having new release detection happen
programmatically so I don't need to manage it once it's setup. Before I
reinvent the wheel, I just wanted to see if there was a known method of
accomplishing this.

Q. Why?
A. Because I have customers that need access to older OS builds as their
products do not move as quickly as CentOS.

Thanks in advance.

Chris