Wow, crazy that this question is getting closer to being answered in 2010. The polytune is major step forward for people looking to tune like SY does.
I once saw Jeff Martin, of the Tea Party, and he explained how had a protype Gibson that could alternate tune during gigs. So you could go from Open G to Drop D with the press of the button. It was worth about 10,000 at the time.
The Variax by Line 6 technology is getting close. Where they emulate acoutsic and 12 string sounds with the turn of the knob. They also can do electric and even a satir.
A pitchshifting pedal wouldn't work, IMHO. If you have a Boss Tu-2 or Tu-3 then turn in onto Chromatic and it tunes it as it hears it.
He is not Alone