I also had a brainstorm when I dropped it and it started unwinding. I have a lot of binder clips in various sizes, and actually had this 15mm silver one on a chatelaine. I clipped it on the thread, and how about that - it works like a charm!
It doesn't matter whether you clip it ON the thread or AROUND the thread - it's just too wide to go between the arms of the flat shuttle, so it stops it completely.
I'm happy with today's purchases! I can tat with this, or use it as a thread winder, or I can always return it to its original purpose, and wind up some of the electronics cords that always seem to multiply around here!