How do I float 3/4" plywood sheets over above grade concrete without nailing, screwing or gluing to the slab?
you can just rabbet each sheet with a halflap type edge (i would make it about 2 inches wide), then glue and screw through both to attach the system together.  a little more work than usual, but relatively simple once you get going. you can build a simple jig for your circular saw out of plywood to ensure it all lines up properly.  if you drill the upper lip on the edge, the screw will suck the joint up and tight.

FYI, if you are going to float ply over a slab, lay down and tape seal a poly vapour (6mil or heavier) barrier before you put down the ply.  this will prevent moisture from being absorbed by the subfloor and oak and avoid rot and warpage.