What I have done before is take a very small drill bit and drill into both the switch and the broken off toggle trying to get in the dead center of both. Next find a piece of metal that will fit in the holes (I used a finishing nail that I cut to length). Test fit to make sure it the right length, glue it into the switch and let it dry, and the glue the toggle onto the stud thats glued onto the switch.
The one I did was the metal shaft on a pot and it was hard as hell to get it centered but it worked well, good luck

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