I've been trying to figure out how to do this too. I just finished implementing generating meshes without having SkeletonRenderer do it for you (the SkeletonGraphic class uses the single-material version of this), and creating dummy skeletons in an editor is pretty trivial, but I don't know a way to just render a mesh whether as part of the GUI or as a floating thing under your cursor without spawning an actual GameObject (in the case of scene view preview).
I thought Graphics.DrawMesh would be the way to go but results are inconsistent.
Anyway, if you can just figure out how to render any mesh, that'd solve your problem.