Not all that difficult... I end with with the initial IDL render with character bald, and a second area render in progressive mode over that (so the basic frame is the same, you just get that annoying white 'drop shadow' line) with the hair included. In Photoshop, copy/paste the second render over the first. Take eraser tool, soft edges, run around the hair and clean up the now spotty face. Done in 2 minutes.

Again, it is scene/lighting specific. There would be some scenes where a more complex extraction method might be needed. It is still saving me hours.