I'd like to suggest wsusoffline. It's a pair of scripts with a GUI for configuration.
The first script downloads microsoft security updates for various of their products (different Windows and Office versions) and saves them on a CD, DVD or a portable device.
The second script automatically detects the appropriate updates for the machine it is run on and installs those.
The products website is
The product is both open source and under GNU GPL.
It is already portable in the sense that it only stores and modifies files in its installation directory.