Pretty simple. Have a tool that creates the most basic child theme. Users can choose to do it or not.
The suggestion here (https://wordpress.org/ideas/topic/child-themes-to-be-automatically-installed-and-activated-rather-than-parent#post-28778) is for automatically generating and activating a child theme, but I think it should be up to the user.
And instead of having to install a plugin for the incredibly simple task, just make a button for it under tools. Boom. Done.