I don't think this is a good idea. The tweeters need to be behind the listeners aiming towards the front of the room at 45degrees as they are designed, not shooting straight down at the floor. Also, I don't think it would be a good idea for the top/bottom woofers to be parallel to the ceiling.
I guess I'm not sure why you don't want to use an omnimount or some other DIY method like I did, using a cheap shelf bracket from Menards.
I don't think THX, Dolby Labs, etc. would agree with your idea either.
