[trotsky]

You pretty much nailed how it's done, good show for off the cuff. Encrypt file with large symmetric key. Slice into n pieces, where n is like 5-10 or more. Distribute a few copies of each slice to reliable people unlikely to directly conspire. Distribute encrypted file widely. Give instructions on how to gather as a group based on some basic trigger. The chance of the gathered group missing every copy of one of the slices is pretty low as long as nobody gets a master list of key holders.