You may find it easier, and more solid, to create a loop and L-bracket that sits around the threaded stem at the base of the mirror, and use that to mount your camera. Putting any weight along the mirror stem will just amplify vibration...
I've already tested (many thousands of miles) having the lens mounted up on the portion of the stalk, there is no vibration either in the mirror view or camera video up to speeds that we'll not mention.
I'm using the INNOVV bike cam and I have to say it works perfectly, no shudder or vibration and it records at full HD. The nice thing about it is that the control unit is remote from the lens so you don't have this box sitting out there ala GoPro. I can also change the lens to a narrow field of view in a about a minute. As mounted, I can swivel the lens 360 degrees so when I stop and want to shoot some other view it is easy to do. The camera comes on when I switch on power via the Gizmo Dash. It has its own battery inside the control unit which is pretty small and can run for about 30 minutes without any external power source. As it is setup, when I switch power off, the camera does a clean shutdown automatically. I have a 64 gig SD card in it so I can video for many hours and the control unit is set to recycle the storage.
I bought two of these cameras and I'll mount another for a rear view and stitch the video together show side by side front and rear views.
The L Bracket or loop around the base doesn't allow for video capture of the speedometer and tach which are mandatory for my needs. In my videos, using the wide angle 120 degree lens I capture not only the view ahead and to the side but a full view of the speedo and tach which is important as the viewer is able to see the speed the Norge is traveling as well as where it travels.
This is a picture of my newly modded stalk bracket but as you can see it would be cleaner if I just drilled and tapped the into the stalk and then mounted a small plate to which the lens could be affixed. The lens is very light and I could even go 10 or 8-32 for the threaded hole going only 3 threads deep. I have a tiny 2 axis gimbal that would still give me the 360 degree rotation as well as elevation movement if needed. My other solution was to take a piece of alum stock and drill a hole to accommodate the stalk diameter and then drill/tap for the fasteners and then cut it in half for a more encompassing bracket but without a working bandsaw, it's tough work to cut that much material.
I do not have access to a mill anymore so this was made up using a dremel and hand file. It works really nice and if I kept it that way I'd coat the aluminum with a black paint to avoid the "look at me" effect of the bare metal.
The upper component with lens attached: (once mounted, the assembly can't be moved by hand without using a great deal of force)
The lower:
and assembled and mounted:
