Nope, you're stuck.
I'd suggest that when it's done, you disable updates to that game. Right click the game in your library and go into 'properties' - look around, you can't miss it.
When you DO get to a broadband access point of some kind, you can turn it back on to apply any updates that may have come out since your last check.
lol 'When it's done'
Is it going to be possible to download patches outside of steam (from bethesdas official site or anything) and put them on a storage device? If not that seems kind of ridiculous.... I know dial up users (or even satellite users with bandwidth restrictions) are a rarity these days but forcing these kinds of things is absurd. I've been an avid PC gamer for over 12 years and I've never experienced this. I've read other posts and realize it's to help prevent piracy (which is probably impossible btw) but all it really seems to accomplish is aggravate some or make the game entirely unplayable....
I don't even care about all the posts concerning bugs. Almost every PC game I've played has bugs on release date. I usually just get patches from friends who live in the city and have cable access. If I'm not able to do this I guess I may have just lost $50 heh