How to secure lights mounted upside down

I've got six hella 4000's
Four up top and two on the bumper

Agreed they're designed to be mounted upright, but they would look goofy as hell mounted upright on my front bumper.
The ones on top are great and rarely need adjustment but the bottom ones constantly vibrate themselves till they point up way too high to use.
I know other "old school" lights have the same issue.

Anyone have an idea how to secure them so they'll hold their aim? I don't want to take a wrench and crank them down too tight. I've used the Allen wrench to do that as tight as I was comfortable with but they still wind up pointing up again.

Suggestions?
Thanks!

 

You might try using blue loctite on the threads of the mounting bolts.