Experimenting getting the work of two lights out of one using composite images.
I took two shots with the same settings on a tripod, held my SB700 w/ umbrella at the left for one, and the right for the other.
I overlayed the images in GIMP as two layers, and set the top one to "brighten only," then applied some curves and the like to give it a bit more contrast. While I was at it I added some red/yellow to the highlights and cyan/blue to the shadows, just the tiniest bit.