I have recently purchased an archtop jazz guitar with f holes. I wonder if it might be possible to have the X fold and spring back into position through the f hole.
Something like that potentially help, but I'm not sure that the diameter of the magnets would allow them to pass through the holes.
Maneuvering the brace once inside would also prove extremely difficult.
We've seen folks use velcro on the back of instruments that won't accommodate for the brace, but it may not be finish friendly.
Have a look at this thread - https://support.tonewoodamp.com/support/discussions/topics/17000013250?page=1
it should work on any instrument, including guitars with small soundholes, violins, double basses, etc. I'm going to try it on a bunch of my guitars, including a few jazz boxes with f holes. Fingers crossed!