jordan rudess using his keyboard like an arranger http://www.youtube.com/watch?v=aII0De0ek9k

Notice his left hand holding chords that trigger the guitar strumming that follows his chords and trigger the vocal programme.

Changing right hands sounds just like a registration or one touch setting......

Is it beyond anyones imagination to see a performance like this being done on a true arranger with some moderate tweeking ......

Just needs an open mind.