Hi Burr,

Not sure, but maybe this thread I'd started might help you in some way?

http://moi3d.com/forum/index.php?webtag=MOI&msg=3140.1

Something you can do within 3D-Coat with Voxels is a Boolean Difference" type of thing.
It's called "Subtract from"...it subtracts an object on one Layer from another Layer.
This means you can bring in your basic Primitive model shape, convert to Voxels & do the surface details.
Then you can "Subtract" other objects as needed before you finally Export it out as a STL for CAM use.

This was something I'd been playing with when making ring bases & needing to sculpt on the top of them once in 3DC.

HTH, Colin