Thanks for chiming in Matt. Neat idea, and I remember something similar from doing with RT as well years ago, but then using an ambient an a GI. I'll try that. It is actually comparable with an invisible sphere, and might take less time. We'll see. Maybe less grainy too.
And you are right about the exposure. In photography it's also not always easy to get darks and lights in balance, and (nice) darkroom work was necessary. The HDR filter works pretty nice too, done carefully.
My guys (and girls) already have an adjustable tan