On the plus side, scanning an entire roll of 120 film is pretty fast. I didn't cut the film so it was simply a matter of moving the film underneath to the next frame and taking a shot. At f/16 in manual focus mode pre-focused at the correct distance, there is sufficient depth of field in case the camera is not completely on axis.
However, not being on axis is one of the largest problems with this current setup. I found it extremely difficult to align the camera such that the entire frame is level with the film. A lot of my shots had some kind of skew. It's not the end of the world, but it's also not ideal.
Since the 120mm macro lens isn't 1:1, each frame will need to be cropped of the excess dead space. For the 6x8 frames I shot, the crops were still 8000 x 6000 pixels, which is more than sufficient. Editing the scans is still the same as with the scanner; run the image through Color Perfect and tweak as needed.
Probably the only strange side effect is that the EXIF data will correctly label the image as coming from the GFX 50S as opposed to coming from a scanner. I suppose the EXIF data could be corrected afterwards, but that was more trouble than it was worth.
Here are some of the color corrected shots using this setup: