A well placed reflector works great to bounce back the one light for better coverage, an effective cheaper option for tight focus situations...you can reposition the reflector to direct the light with one hand and click the shutter release with the other, different light for every shot if you want it.
The next thing that would blow these shots to alpha-dookie level is using some L-series glass... I'm Nikon ignorant so whatever the nikon equivalent is to the Canons' luxury glass lenses... The difference is simply stunning!! My wife is a portrait photographer, after getting the L-series lenses her work took on an altogether more dramatic look... and her fees increased proportionally. I'm not sure if you have the training, but you seem to have the skills, pro lenses would be money well spent!
