Great question
Not sure if the ball mount can be removed ... and gluing another magnet is out of the question.
Thinking out of the box ... adhesively bonding a similar size magnet to the back side of a suction cup might be possible.
Magnets are available at most hardwares and magnet strength will be important to support the camera weight while driving.
The most questionable part will be the suction cup ... it has to support the combined weight of the camera and magnet during x, y and z vibrations
Good luck