I am assuming they are using the Dutch release as the source for all footage seen in the International cut. They would just be using the German cut transfer for the scenes that exclusively show up in the German cut - in which case fake grain unfortunately seems necessary, so that the DNR'ed German footage blends in with the grain-intact Dutch footage.

Which reminds me, have you given any thought to how you will be handling the shots which run longer in the German cut? I think those comprise most of the additional footage. Will you just switch to the German cut for those entire shots, or can you figure out a way to blend the two sources together?