That's some pretty bad luck. There is no way to continue a download from where you left off. Apple doesn't want the download to get corrupted, so they redownload every time. You could try going to Settings-->General-->Software Update on your iPad, and download the update from there. I'm not sure if it will help though. Otherwise, I would suggest going somewhere with Wifi (Mcdonalds or something) and doing what I said above on your iPad itself.
Get something to eat though, it could take a while.