Attached Link: http://www.3drender.com/light/3point.html

Here's a tutorial someone posted in here on the 3-light set up. It's basically the same thing that professional photographers use, except that they bounce their flashes off some other object to make the light more diffuse, rather than lighting directly like in the tutorial. I suppose you could point the spotlights away from your subject in bryce toward cut open spheres or something that bounce light back onto the subject when you turn true ambience on, but I suspect that direct lighting with soft shadows would accomplish the same results with much lower rendertimes.