BitTorrent doesn't work like that. To "seed," you don't need to reupload the entire file - whenever you're connected, as long as you leave the file there, it will continue to be seeded to other users as needed. If you don't think you'll otherwise have reason to connect to BitTorrent in the immediate future, just leave it connected when you're away from your comp - no issues with it consuming your bandwidth that way. Also, part of the magic of BT is that it will only take weeks for the enduser if you're the only one with a copy - otherwise it could go much faster.
Thanks for keeping file sharing fair and... sharing.
