It seems like some of the difficulty comes from trying to calculate the the contour as a vector rather than a raster image.
I would think that a method that only calculates the contour up to a given resolution to be much easier. Rendering the model using location mapped to color and then a post processing step on the image seems like it should be able to do the job.
It is almost certainly easier (in practice) to perform an edge detection or similar post processing step (usually on depth and/or normal map) in image space to get something that looks like the occluding contour. The utility of that data is limited, however.
At the risk of getting semantic, I'd argue that the raster representation of such a contour is not the contour. That is, calculating the contour as a raster image is just calculating something different.
I would think that a method that only calculates the contour up to a given resolution to be much easier. Rendering the model using location mapped to color and then a post processing step on the image seems like it should be able to do the job.