Well, I wussed out and bought the Sonore. The discount made it worthwhile. I also bought and installed the RACO leveling plate. Wow, my plugs have never had it so good. (I tried to post a photo but I don’t see how to do it. The ’gon link asks for a URL.)
I may still experiment with making my own, for fun and for future applications. There are actually a few outlets around the house that could benefit from this type of plug support. I’m surprised that these types of holders aren’t more common. It seems like something you would find amid the vast array of cable management accessories.