Godfrey
somewhat colored
Assuming there was a way to do this, a RAW image has not had anything applied to it; to name one, how about the white balance.
It's just a bunch of data, it's not an image until it has been processed. There isn't even a standard raw file format...every manufacturer has a different way of encoding the data.
Said another way, printing from a raw file (presuming the printing application can understand the file format) would involve that the printing application do the raw conversion and apply whatever adjustments/calibrations/etc were appropriate. That puts the raw to RGB processing conversion back in the hands of the camera or printing application, and out of the photographer's hands.
At which point, you might as well use whatever in-camera B&W image processing settings you like and print from the JPEGs ... I bet the results would be identical. ;-)
G
(Another way that this is done occasionally, with big hits to image quality, is that the printing application simply extracts the in-camera JPEG preview from the raw file and prints that. Again, no reason to print this way rather than just used the camera's JPEG rendering for B&W that you like in the first place.)