How can I fool my Mamiya M645?

A month or so ago I loaded a roll of 3200 into my M645 1000S for a twilight excursion. I ended up shooting only 6 frames before it just got too dark even for the 3200. The next day I wanted to shoot some Ektar 100, so I put the camera in my dark bag, pulled the insert out, put it in the plastic case, and put electrician's tape around the case seam. I figured I'd just use it up at a later time.

I then realized that when I put the insert back into the camera, it'll think it's a frsh roll, and I'll have to advance it until the counter says '1'. Hmm. That'll probably be pretty close to the end of the roll, defeating the original purpose of removing the insert with the half-shot roll.

Is there a way to fool the camera so I can actually use the remaining frames? I was thinking of putting something against the little button that tells the camera that back was opened, the put an empty spool in, taking shots to get the counter to 6, then swapping the insert with the film in it. Is that possible? Anyone have any other ideas?

In the dark, roll the film manually back onto the original spool.

Then put that roll back into the insert and, put it back into the camera. Advance to the 8th exposure using a lens cap to prevent any double exposures.