Impulse is the only method to obtain just the updates. You can use Impulse Anywhere from a PC that has internet to download the most up to date full install. This can then be copied/installed to your offline PC.
http://anywhere.impulsedriven.com/Default.aspx
You will need to have your Sins serial registered to your account before you can do this. With your internet situation, the easiest way to probably do this would be to write [email protected] with your serial and we can add it for you.
