Where do you live, the middle of the jungle? Generators lol?
She lives in the wilds of Alaska. You should see some of the stories she has from when delivery people try to find her house.....
However, borrowing a friends Internet Connection is the way to go. Note, if he does not have the MS Wireless Dongle then he will need to get that (not cheap) or a wireless bridge (bother to set up) if he goes the wireless route. The best way for this ad hoc connection is to use an Ethernet cable to the friends router or cable modem for the updating.
As an aside, do the newer versions of the 360 come with Wireless built in?