If there's no orange mask, perhaps some orange filters could be made from unexposed but processed negative film. As far as I know, it's just a constant orange dye with equal density throughout the neg.

Another advantage of MP film is that you could make slides from your negs by shooting the negs macro. I've always wanted to do this, but the orange mask poses a PITA.

Side note... why does motion picture film use 250 and 500 speed designations? I'm curious why their conventions would be different than still film.