For me, pre-flashing *film* is not a viable option: it would mean re-rolling 120 - something I have never been able to do.
Ed - not sure what you mean? Do you mean pre-flashing the whole roll? I use roll film and only pre-flash the frame I'm using through a double exposure (1. flash, 2. image), some images will be pre-flashed on the roll, others wont be. Have i missed your point?

cheers

Leon