Comment Apple Caching Service (Score 1) 159
On any Mac in your office, running 10.8 (Mountain Lion) or 10.9 (Mavericks) purchase (for $20 or so), download and install the OS X Server app.
Turn on the Caching service. Problem solved for Apple devices.
The server then registers itself with Apple, they see the registration coming from your IP, so when further devices from that IP address request a software update, these machines are pointed to your internal Caching server. Then, when a device (or a Mac) tries to download an update or purchase something from the App store, it will come from the persistent cache in preference to the WAN.