As far as direction goes in the normal HDR in Bryce - I've created a workaround for that already. I just group the objects including the camera and then link them to a hidden cube. I rotate the cube like a giant turntable and aim the light where I want it. This totally preserves your camera angle and just moves the shading to where you want it. You can even see it update in openGL. For some reason this technique does not work with my pure white light... : /