And the mirrorCamera is looking the right way! The following doesn't do anything other than paint the mirror's plane yellow:
Projector mirrorCamera = new Projector();
TextureManager.getInstance().addTexture("Mirror", new Texture(256, 256, Color.yellow));
TextureManager.getInstance().getTexture("Mirror").setProjector(mirrorCamera, true);
I'm just going to use the projector as a camera, render into an Image's graphics, then replace the texture on my mirror, or is that WAY too stupid (expensive) a method? But either way, as I understand it I would need this for the software renderer anyway.