Struggled focussing on the description a bit when Gwen was making frequent references to the "bunt", but apart from the pronunciation the context was pretty clear that by "bunt" he meant the board.
I think a bit more focus on using the body as a pendulum would be useful.
The way I look at it, you need at least a little speed. I commence the pump cycle by transferring weight from the front foot to the back foot and pushing both down. This changes the foil to a climb angle. Starting we are going slow, the climb will quickly bleed of power. In the brief moment the board is trying to climb, I crouch slightly down. This de-weights my feet and eases the climb of the board. As the board speed quickly drops I re-weight my front foot to flatten the board. This permits a very brief glide. And then I restart the cycle, Pulse the back foot and both down as I stretch up, crouch down as the board rises, flatten the board with the front foot, glide, repeat. max power is needed in the climbing phase so use the wing to help a split second after pulsing down with your feet to help your rise and additionally de-weight your board for even more climb of the board. This works well for me.
Alas, I'm no longer young, wiry and athletic but the technique absolutely applies!