This trick brings up a lot of skaters I'd usually rather not think of, but oh well. Chet Thomas used to do sw fs 540 in miniramps a lot, don't know if he ever did one without grab though. Even worse, I distinctly remember a berries clip I saw many years ago where Donovan Strain did one on flat. It looked about as yikes as it sounds.
I remember Vincent Alvarez doing cab 540s without grab somewhere, that's the same turn but popped fakie.