Hi, Jim!

I use the rubber cap from the socket and put it on the shorting plug side then cover it with the pilots seat or inside a compartment with a hinged hatch that compresses the rubber cap to about 33 percent of the height. Or even a desk lock keeper keeps it under control or a bit of firm foam will surfice.
Though I've never had one come loose from even the big gassers or the high rpms of a tuned pipe .40 through .90's in ducted fans.

Or you could use the 5th position (the center pin) Thread the socket there 4/40 then run a
screw through the plug into the socket...course am not worried about it as it takes a good deal of force to remove the plug.

If you try one, I think you will agree there is not much chance of one coming loose in that situation.