Here’s my setup.
I have three camera mounts now, one from the front of the handlebars, and two from the bar ends.
My GPS sits just above the front camera (though I have a mount on the stem as well as the out-front mount, because I have noticed a significant signal loss when the GPS is right above the running camera).
Here’s a close-up of one of the bar end mounts. It’s taken a few iterations to get to this stage, and these aren’t field-tested yet. The previous version stuck out about 3" on a mirror mount, and that vibrated a lot. These are basically two rotating GoPro-style mounts (joined at the circular part in the middle), and a wedge to solidly bolt it into the handlebar. This provides three axes of motion to adjust the camera to be level at any angle of the circle. I have been shooting at ±60° from forward rather than 90° to avoid too much motion blur.
And one picture with the camera mounted.
These are all the pieces. The bolt, two black wedges, and the cylindrical bolt are from Mirrcyle mirrors (Amazon page). The Specialized disk and the piece above it are modified bar end plugs (the plastic disk is cut down). The silver ring is a brake washer to offset the GoPro mount from the bar end plug.
Hopefully these mounts work well and don’t vibrate. Here’s a sequence using the previous setup. When I manually process the pictures, I offset the three sequences by 0.1 seconds so they’re not in the same position.