Nice piece of work.
I would just like to point out that if you are using apache. Mod_Rewrite can do this verry easily. ( mod_rewrite is awsome if you don't know about it, and you run apache you should check it out!)

As well SQUID is a proxy and can be setup as a reverse proxy easily.

I know these aren't all ontopic about perl, but I feel both these projects should get mentioned if someone may hapen upon this in a search.