I have neither the experience nor the training to teach this.

I will therefore just relay my intermediate-level experience in the hopes that it may help.

I found, with time, that there is an increasing degree of precision of pedal mechanics that comes only from practice. What I used to consider a smooth pedal stroke may have been enough to keep me going in a straight line on rollers, but it wasn't as efficient as I could be. I re-vamped things ever so slightly, and focused a bit more on the "mud scraping" part of the stroke. (The mental imagery I use is different. I think about loading the heel cup of the shoe rather than the toe)

One positive take-away from this was that I began to think more precisely about which parts of the pedal circle I am in, and where to direct the energy toward maximum efficiency. It took the better part of an entire season for it to become, say, 50% intuitive.

I understand the feeling of the feet sort of bouncing up and unloading the pedals as you speak of. This doesn't really happen for me any more except for the following conditions:

1. when I am incredibly fatigued and the mind wanders into the realm of "I don't want to do this any more"

2. when I do very fast pedaling and am unable to relax (140rpm or more for me, depending on how much I have been training this. Sometimes I can exceed it smoothly, sometimes not)

It all took time, but the main focus was increasing the efficiency of my mechanics to the effect of minimizing motions that pushed the crank in any direction other than tangential. I never "pull-up" on the pedals.

With that said, I still have a long way to go.