Have you tried to use a uniform background? I have successfully processed many turntable scans in RC. All I did, was use a kompletely black background using black fabric and having it as far behind the object I was scanning, so it would not be in focus. Then I lit my foreground object in a way, that the background did not receive any light.
I also use cross polarization for the lights and the camera to make sure I eliminate all specular reflections, also on the black clith in the back.
If all that the camera sees is the object and the turntable, this works like a charm.
Cheers
Guillaume