I did it using a railing:
(Sorry for the dirty car
Here’s what I use besides the Mi sphere camera:
Mount + Adapter
For securing the setup: Magnet, these metal ropes and zip ties.
The railing was the cheapest I found and considering that it’s okay. It’s making noises at 50+kmh because of the bottom being open, but I don’t care too much.
The ishoxs stuff is great though. I was sceptical that the camera could bend backwards from the wind, but it survived 100kmh. Didn’t test anything above that though.
The magnet has exactly the right strength for this. It won’t fall off or move no matter what you’re doing but you can still get it off with enough power applied.
I’ve attached a cable to the camera and wrapped it around the setup a couple of times to secure it, then went to the interior through the passenger side window.
All in all I’m happy, now I’m just missing time to actually use it. Couldn’t take much pictures with it yet, but here are some examples. Unfortunately I messed up the camera’s resolution setting so the pictures aren’t as sharp as they could’ve been, also I didn’t notice the cable is so far in the picture. Next time I’ll do better pics, this ride was more or less just speed testing the setup anyway.