Web forwarding proxy in C # or PHP available?

I have a shared server web host in the States (I'm from the UK) which allows me to publish PHP and .NET applications. I cannot install my own software on a remote server, but I would like to set up a forwarding proxy to access sites that serve different content depending on which country you are in.

My C # and ASP.NET skills are fine, but my PHP is very limited. Are there any solutions that someone would recommend for this kind of problem? The proxies I've researched seem to require installation on the server machine itself, whereas I'm just looking for something accessible from the URL.

Obviously, as requests come in from the UK, the headers must be processed by a proxy before being sent. I was going to code my own HTTP handler in C #, but I don't want to reinvent the wheel if something is already there;)