Great video, Andrew ... and a wonderful image too.
Why 2 negatives, though? I would think with a properly calibrated digital negative workflow, you could achieve everything you wanted image-wise in the editing workflow, and then output to a single negative.
I could see how you might want to do it if you were printing directly from a tricky film negative, where the dupe copy makes the adjustments you need, but I'm not understanding the need in a digital negative workflow.