It's entirely possible he is merely sending his color negs to a lab and requesting a b&w neg in return. If so, they are probably doing it digitally -- a very easy process. As you may know, many, many alternative process print makers use digital negatives. But like Konical said, they way it was done in the past was with Kodak's Panalure. It is possible to print a color neg with a VC paper, but I've never seen a satisfactory print doing it this way.