I've dragged iTunes over to the TV, leaving the menubar on my MBP. I can't view the visualizer in full screen mode cos it seriously affects my MBP display, and doesn't show on the TV. So I have the visualizer playing in-window mode and I've just manually adjusted the size of the window so pretty much all one sees is the visualizer.
Now, all I need a way to control the music from 'behind-the-scenes'.
EDIT: In response, to your edit. Thanks. That's exactly what I need. Made my day, you have.