On which operating system are you, first?
If you're on Windows XP, don't think there is a way, if you select the full screen one, it will get on top of everything else, including the reduced one.
Maybe something could be done with reduced-opacity windows, dunno.
You could only use the reduced one if it's on top of the full-screen window...
afaik
just thought of this, if it was possible to modify priorities, you could make the reduced one always be on top, just like the windows task manager does...