It seems to me that one of the fundamentals of hypermiling is to keep your foot off both the gas and the brake pedals, as much as possible.
So how does using two feet help in this matter? Assuming it's an automatic, using two feet isn't necessary to drive.
I don't know about anyone else's driving style, but I use only one foot - and it often pivots and hovers above either the gas or the brake pedal,
without touching either pedal until necessary.
Utilizing perception, foresight and intuition helps in deciding which pedal your foot should hover over at any given moment.
