You can add the service pack from anywhere. The restore CD has the key and will match it up with the computer no matter what else you do. To be honest, while it does take a while for the new updates, I don't see why that is a huge deal. Just start the download and have a beer, do another and watch a movie. Do some over night. Now if you had 10 computers then you would do one as above and image it so you wouldn't have to do those.
Can't you download SP1, thus getting all of the previous updates?
