You have to be picking up your entire leg with a slight rotation in your hip to be able to yield and NOT put weight at your hip. You are still sitting square on your butt and swinging your leg.
1) sit in a chair with 4 legs. if it has a hard seat even better.
2) yield as you normally would, pretending the front leg of the chair is your horse.
You should be able to notice that your butt doesn't move on the hard chair.
Now stop a moment and take a deep breath,
This time try using your ankle to yield with. ( i am always barefoot in the house so it may be different with shoes on.) I "think ankle" but my calf actually hits first.
When I do it i roll a bit to the side, nothing major just a slight weight shift. (i'm using my right leg to explain this) I can feel my weight shift past center (by crackie!

) to my right cheek. I guess technically my spine has to move a bit too. Just a small move tho.
To the best of my limited knowledge the horse will begin to anticipate the cue for yeild by the shift in weight as well as the tap.
The weight shift says "ready" and the tap says "go"
Let me know if this makes any more sence. If not I'll try again!
(my chair is really getting good at this!!!!

) j/k