I built a script ages ago that would act as a simple proxy for a defined site, but allow text replacements.
So you could set it to mimic the bbc and replace the word bbc with something, or replace images etc.
I'll be working to improve the lib as i wrote it a few years ago and not long after then the project it was needed for disappeared. But i really liked the idea of it so here's the current repo:
I have a few todo's on it, like adding regex replacement support, and simplifying the code a bunch.
But check out the repo if you want to contribute or try it out. Its got a simple xml file for config currently.
~ UPDATE ~
Since writing this i've replaced this project with Ditto.php, info here: