You will have to haul your gaming pc to work (or any place with a netconnection..cybercafe,friend etc.) and install the game that way. Once done you can tell steam to start in offline mode and from then on you can stay in offline mode.
It does mean however that you won't get patches so you'd have to connect to the net and let steam update the game when you want your game patched.
Also as offline player I suspect you will want to play playermade campaigns which you'll have to download on a USB-stick and then place in the right folders on your home pc...the stock content isn't that big for singleplayer ,just 2 campaigns, 5 single missions and 24 quick missions. (Unless you make your own missions in the FMB which would keep you busy for ages.)