Don't try to make the second h happen....
P.S. Love that clip of the sprinter start! Given the way a sprinter starts, I would agree with you that you don't need to focus on making the second "h" happen, but pitching isn't starting exactly that same way. With pitching there is definitely a purposeful kick out with the stride foot, where with sprinting it appears to be more a focus on the stride knee with only a slight reach with the stride foot.
Given Colin's picture example and comments about his DD's focus, I'd bet she is not taking advantage of pushing with both legs. I'd bet that her focus is powering the drive primarily with the pivot leg. If she tries to fix something later in the sequence without correcting a factor that contributes to the second h, I think it's a misguided effort.
Try both ways: force a second h from a one leg drive and see if you can get detachment from the rubber by 3 o'clock. Then see how much easier it is to get the h and detach if driving with both legs in a bang bang fashion.