I wouldn't......and as Kathy says, you don't need to. I HAVE used the spray on the edges, when doing an edge to edge design just to keep the edges from flipping. But that was only when I was using a design that had a lot of off and ons on the edges. It was a pain in the bxxx. I prefer a few pins on the sides and that's all. As for floating the tops and not pinning the bottom. I've seen where you get some special "grips" to hold the top layer down. I use them for my "testing" quilt, but not for good quilts. Seems it doesn't hold the quilts as well.
The grips are on this page:
http://myqbot.com/notions.html