Been there done that, it's not quite that simple. The LCD only works in an open DuoDock when you've cut power to the Dock's Declaration ROM (or removed the ROM entirely from a Dock+ ZIF Socket) because the DeclROM tells the Duo where it's Docked and to keep the LCD shut down.
Blasted thing also tells the Duo that stereo sound's not avaialable and it's the devil's own time to get stereo output up and running using an SAII NuBus Card.