I haven't made it, but the host of Booze Traveler walked through a sake brewery in Japan. Instead of using enzymes in a mash to break down the starches into sugar, they use a mold that they said was also used in the making of soy sauce. So it's been in use for a very long time.
I suppose you could buy the mold and try it at home, but I've never looked into it. It requires temperature and humidity control, that much I know.
The mold contributes to the flavor. So going through a mash to break down the starches wouldn't have the same result.