It might be a simpler way to make two separate renderings, one in wireframe mode, the other using a shader of the colour you want the opaque parts of the object to be made of (disable shadows it you don't want any), then photocompose the two as layers in a photoretouching program. If you use Photoshop you might be able to achieve the final effect with just a little actual pixels retouching, aimed to erase with a dark colour the white lines that outline hidden polygons. Then it might be enough for you to take advantage of an appropriate layers mode (the drop down menu) and mostly of the layers options (the blend sliders), since there should be sufficient contrast between the white of the lines and the dark colour of the opaque parts for the blend settings to operate appropriately. Cheers, Orio