There exists a DIAS-like design that adds a “happy switch” to a Glock. Working models exist (outside the USA). Blueprints are available if you dig a bit. 3D printing comes to mind, if $200 and some paperwork make legal problems go away.
of what possible use would an uncontrollable FA handgun be?
I may, or may not, know someone who has the Glock backplate mod blueprints you are talking about. Lightning link plans too.
Note: this person is NOT me...