I've never seen anything that suggests that dual screens can work like this, although I have seen some people trying it. I think the issue is that the Orbiter you are looking at is the "On Screen Orbiter" and that is designed to be on the same screen as your video. There are other Orbiters as well, like Web Orbiter and Mobile Orbiter that you can put on mobile phones, web pads, PDAs and your laptop/PC - this will then allow you to pop up the orbiter menu system and do all the normal things without affecting the main display and its video, or even use the On Screen Orbiter of another MD! That's the point of the Orbiter, its can go whereever you want to control from (as long as you tell it which MD you want it to control using the Room: button down the bottom)
But not on a second screen, I believe, as this is the same PC and so it will put it on the main display. Conceptually, putting it on a second display is quite a different thing from all the other options I mentioned above, but I agree it would be nice if it could do it - perhaps log a mantis request? You would get the same effect you are looking for, and probably nicer/more effective by using a touch screen web pad with wifi, and it can do that right now - however this is obviously going to be more expensive!