Sorry to have to give you the news, but all the tricks I've tried really don't work. There are some people working on partial file sharing that might help in the future, but for now, it's just less hassle to start again. The same thing happened to me with a rare 185 meg file. I just laughed! Oh the irony--this was the third time in two months I'd gotten that close. It's getting to be a game.

You can just leave it in your incomplete folder and start a new search--sometimes (not often) LW will pick up where it left off. Sounds like you already tried the "resume" button in the Library pane.

[edit]--you can often play what you have with something like vlc