Sorry for the delay in posting these; it was a busy weekend. I didn't take a picture of the M3 boot as I was removing it from the ring but here are some pics of the M5 boot as I was trimming it and shaping it for the M3 ring.
I started by hanging the knob between my knees and fitted the ring to where I wanted it. Then I folded the leather over the top, held it with the clamps, and cut small slits where the tabs would poke through.
Then I trimmed off the excess leather leaving small flaps to go around the plastic tabs of the ring.
I used Gorilla Glue and would put it on the boot/ring, clamp it, and let it sit for at least 30 minutes. Then I would move on to another part and continued to trim off excess leather.
These last two were near the end; I didn't take a pic when it was fully finished but this should give you a good idea of what I did. The leather is glued to the ring and trimmed off at the edge of the plastic ring. Only the little flaps that go over the plastic tabs go over the ring.
In the end it all worked out great with one minor exception. The leather of the M5 boot was thicker than the M3 boot. This made it very difficult to get the plastic tabs to click back into place on the center console trim. I ended up pulling the center console off, turning it over and clipping the boot back into place. It's a tight fit but it went on and I have no concerns about it coming off.
Was all this necessary? As others have shown, no, it was not. I worked on this over the course of about 4 days in the evenings after work. The same thing can be accomplished by just poking holes for the tabs and snapping it in but I wanted it glued to the ring like the stock one was ensuring it would never slip or move. Plus, it was more fun to do it this way, for me anyway.