We describe a novel technique for simulating a cinema projection room with arbitrary dimensions in a realtimegame engine, while controling the camera interaxial and convergence parameters with a gamepad controller. Our technique has been implemented in the Blender Game Engine and tested during the shooting of a short movie. Qualitative experimental results show that our technique overcomes the limitations of previous work in stereoscopic previz and can usefully complement traditional storyboards during pre-production of stereoscopic 3-D movies.