Good point - it probably goes well beyond guitars! And though we would love to see how they do it, part of the secrecy is probably to protect intellectual property.
I think you're probably right about the process being something akin to the roasting technique - perhaps at different temps, maybe for different durations, etc.
The two techniques seem to be different means to the same ends. I.E., more "alive", resonant tone.
But Yamaha's process certainly stops short of giving the obvious appearance of the roasted technique - at least not the necks.