I've got a couple of the MPI swtich/jacks and haven't had a problem with them. I also have several of the Great Planes switch/jack holders with the silver push-pull rod. I have had trouble getting my charge jack to stay in place on one of those.

Maybe you could try a short servo extension, with a slightly different plug? My battery tester wouldn't fit into some of my jacks, so I stuck a short JR servo extension on it, and it fits fine. I am not sure what the stock plug was supposed to fit.

Good luck