Speaking of Stephen Stills, I saw him at the Santa Barbara country bowl, way back when, maybe late 70s? I think Finnegan was playing keys.
I always remember a section where they were jamming out, and Finnegan plays a chord, can’t recall which hand - - but with his free hand he moves some kind of a slider switch up and down, and the entire chord changes key multiple times, i.e. up a half step, up a couple of steps, back down - - all super fast and in time - was really cool.
Does anyone remember a trick like this? No idea the keyboard, but believe it was some kind of synth, maybe the big Yamaha CS? I’m sure this could be replicated now programming a slider or knob.