I'm thinking one thing that could help is standing behind them while they're hitting off the machine and giving them verbal cues to help timing/sequence. Basically just stand back there and say "load, stride, explode..."
I'd simplify this even further. If you're giving them 3 commands for each pitch, you now have to time your own commands with the machine, and hope the player reacts in a consistent enough timeframe to be on time with the pitch.
Consider just telling them to "start moving earlier" or "get started earlier". You don't have to go all "Newtonian" on them with the explanation, but even something as slight as a simple weight shift or rock backwards gets them in motion before the pitch (which also encourages the Yes-Yes-No approach). I think we need to let them figure out the "explode" part of the swing on their own, and believe this is infinitely easier for them once they realize they need to start moving earlier.