Thank you for this John. The Velocomputer sensor's mount is what I am looking for. $50 is pricey though.
I've wrapped the Garmin mount around the hub twice and was thinking of twisting it to take up some slack as you have suggested.
Wahoo has a shoe mount for their RPM sensor that should fit the actual sensor piece in the Garmin wheel hub mount once it is removed from the rubber mount. The Wahoo shoe mount is rubber and mounts through holes through which one can run the laces of the shoe. I used those holes with zip ties to mount it to my cranks. Since the hub is much more protected by the spokes, you could use the hand releasable zip ties cut to length to make a very nice mount for your sensor that would be much more svelte than Garmin's rubber housing. In fact, I'm glad you brought that up, I'll give that a try in the spring if Wahoo doesn't release their wheel sensor.
I didn't know the Garmin sensor used a magnetometer instead of an accelerometer so thank you for that information. I'm actually surprised by that, the cost of accelerometers has been driven into the dirt by their inclusion in smartphones to the point where they cost less than a quarter a piece. Magnetometer or accelerometer aside, I am really happy to see the demise of the Hall Effect sensors that have been in use for decades with all their alignment and proximity issues. Been waiting for that for a very long time.
Both Wahoo and Velocomputer are using the Nordic Semiconductor part that contains the CPU, memory, radios and software stacks for both BTLE and ANT+ and transmit on both protocols simultaneously. Both devices readily come up and answer to the utility that Nordic supplies to modify the flash memory on board.
I have one of the Velocomputer sensors and don't think it's ready for primetime although it's promising. The mount has some really nice features like it's size and it's bevel/radius mounting to the hub. However, the ladder-like rubber strapping is a bit fragile and easy to break. That's why I think getting your hands on the Wahoo rubber shoe mount and using that to mount to your hub with hand releasable zip ties would solve your problem and be a very clean solution. The Wahoo shoe mount quite robust but not nearly as large as the Garmin mount and it and won't break or tear.
J.