^ Okay, maybe you have an unusual car, but the majority take a lot longer to remove, reinstall, and re-aim, than the 2 minutes it takes to tape them off and throw a piece of cardboard or a tarp over the engine bay.
How long did it take to post this topic and devise a way to hold them down? Why do you even need to hold them down? They don't wiggle around much while you're polishing. They even seem to like it, like petting a dog.
Be careful, if you go at them very aggressively with a power tool they can end up with a hazy surface from heat, then you'll have to start over to remove that. Otherwise, you could have just put on an old pair of pants and held them in your lap.