If you combine the ideas. Use one holder per film type. Use a modified darkslide. I think you could get three shots per sheet of film. Instead of trying to get multiple types of film into each holder you'll be getting multiple images. The downside is you risk ruining the first image when you do the second.

The way I see it you'll need three extra darkslides. First one would be cut short by a 1/3. The second would have hole in the middle. The third would have a hole near end that slides into the film holder. You'd need to leave a margin.

The only other thing I guess would be reloading in the field.