If possible(depending on the height of the ceiling) Turn the flash power up pretty high and angle it towards the ceiling so that the angle from the the flash(on the camera) to the ceiling, and down to the head is apprx 45 degrees. This angle can be changed easliy, but 45 is what most people use. Then place something below the head, a white board preferably, to bounce some fill up onto the head to counter the raccoon eyes from the above flash. You won't get a perfectly white background, but from above the flash will spread enough to make it white enough to easily fix in photoshop and no shadow will be cast from the head.
If there are high or oddly angled ceilings, I'm not sure what to tell ya. Since the SB-6oo has a rotating head, maybe turn it to the side 45 degrees, bounce it of a white board to get your main light and have another white board on the other side to bounc in some fill. That will also solve the problem of the shadow you want to avoid, but then you might have issues with a gray backdrop.