Take a look at IPFire updateacelerator and clone it, it caches windows updates, Linux updates, Antivirus, comom regular updates, even android and ios updates.
It's one functionality that is really handy, saves bandwidth, time and its alot better than managing and hacking proxy settings.
Quote from the update accelerator site bellow
Imagine this situation: Microsoft has just released another “patch Tuesday” update, the virus scan software has to be updated and Adobe and Symantec are releasing new updates at the same time. You have multiple systems to update and they all need to download the same files.
The Update Accelerator has been created especially for this type of scenario. It has been developed for networks with multiple clients. The Update Accelerator caches, similar to the Proxy server updates for the Operating System, Virus scanners and the like. The load on the Internet connection is reduced and it also prevents long waiting times when loading updates to multiple clients.