CodeIgniter app to manage hundreds of domains

[eluser]transition[/eluser]
We developed some custom app here with CodeIgniter to help manage all of the domains we own (180+). Most of these domains will have simple 1 page content. The goal I have is to be able to create a single front-end controller on our master domain (lets say it's at /home/master/www). Lets say one of the sites i'm managing is called TestSite.com. This site is located at /home/testsite/www on the same server as the master site. What i'd like to be able to do is whenever someones goes to TestSite.com is to make that request on our master site so we can lookup the associated template for that site and deliver the requested content. I don't want a redirect - it needs to look as though you're browsing TestSite.com even though requests are being pushed to the Master site.

Does anyone have an idea of how I can take requests on the TestSite.com and redirect them locally to the Master without the user knowing? Or is there an easier way to do this that i'm not thinking of?

edit: i'm desperate for a solution here. $20 paypal'd to whoever can propose a workable solution :-)