The stage in the Flash CS4 Authoring Enviroment is a running SWF. That what makes thing like the 3D and Bone Tools to work in the IDE.
Is it possible to access that swf ? I suspect the immediate answer would be no because that would raise some security issues maybe and cause lots of developers to crash the IDE every 5 minutes :).
That said I don't expect this to be a straight forward process, but I guess there should be a way to access that.
Any thoughts ?
I can only tell you how components work on the stage, where we've attempted the type of access you talk about.
I suspect that at their core, the 3d and bone tools are implemented using component-like tech to display the "live" stage instance. In general this would involve a compiled instance of a live preview swf that is placed on the stage. It is misleading to think of the stage as a single player. Each component preview runs in its own sandbox that, as far as I can tell, has no means of communication with other component previews on the IDE stage. There is no common storage location.
Of course, if you were in charge of the preview swf (as with the case of a component), you could try LocalConnection to chat, but the previews you want to penetrate are closed. I suspect if you dig hard enough, you'd find the bone/3d preview hidden in the installation folders (perhaps in a swc.. ik.swc looks interesting) and might be able to hack about at it with a decompiler, but straight out the box, I'm not sure there's a solution to what you ask.