Using a http proxy without manually configuring the browser to use proxy server

  1. Write a PAC file that mimics your requirements
  2. Host that file on a server somewhere on your LAN
  3. Configure your DHCP server to announce the location of that PAC file
  4. Configure the broswers on your LAN to use "Automatic Proxy Configuration Settings" ( In your browser options )

Some relevant links:

http://www-archive.mozilla.org/catalog/end-user/customizing/enduserPAC.html

http://en.wikipedia.org/wiki/Proxy_auto-config

http://technet.microsoft.com/en-us/library/dd361887.aspx