Use a remote control for hoverboard to control the scooter from a distance. With a remote, you can switch the hoverboard on and off, set an alarm, and change it into a 2nd mode that slows down the turning speed (so the rider can go faster more safely).
If you do not already have a remote control receiver on one of your gyroscopes, you will need to solder one in. You can purchase a remote control receiver module which will come with a remote.
Here is an easy to understand image with hoverboard remote control instructions overlaid onto it.