I'm sorry - I am still not clear what you mean by this. McNeel have indicated that Rhino6 will contain enhancements to viewport and the rendering system (for Cycles), so this will potentially allow the easy implementation of what you are after.Vray for Rhino can do it and it's done with the VfR frame buffer. And so my request is, why shouldn't Octane go this way and use the own frame buffer? Would help to keep the workflow simple and direct.
Paul