Intercept requests and modification of the server response

[Smoke]

I want to intercept all browser requests and then add some js into server responses before it will appears in browser.

For example "Ad muncher" is doing it. It add js that removes all ad from pages.

Please give me some advise, how I can do it?

I'm using C#.

I found 2 solutions that may be can help me:

1) www.fiddler2.com But as I understand I could only write my own plugin for it, but I can't make standalone application. And also it is a proxy-type solution..

2) www.tcpdump.org and www.winpcap.org I can't find how to modify server responses, I found some info only about sniffering the requests.

P.S: I don't want to use proxy server for this purpose.

Thanks for any help.