Here's a picture that may help
I did the mod just last week myself on my Nokton. I don't have a dremel tool, so I just used files and worked at it for a few minutes. File the cam a bit, mount the lens, check framelines and repeat until necessary. As it happens, I filed just enough so that both the 35mm AND the 50mm showed up in my M6! It wasn't intentional, but I decided to keep it that way to see if it the added lines help with my composition (I hate angled lines in my photos). If it bothers me, I can either file it down just a bit more to get only the 35mm or I just nudge the preview lever a bit and it disappears.
If you want, I can take a quick snapshot of my 40mm's mount for reference, but the picture I posted should be more than enough for you to work with.