Ray - I do something similar in a series of exercises called mian quan cao - the basic exercises from cotton boxing. Our horse is wider and more "square" (thighs externally rotated so that the center line of the patella lines up with the longitudenal midline of the foot) and our back is kept more vertical. It seems to me that to do the exercise properly you already need to know how to song kua etc.
FWIW, I think it is easier and faster to learn song kua et al in a seated position - I showed the basics to Fong and the gang when I was in SF earlier this year - once you know how to song kua and so on, it is easier to incorporate into any form, stance, or exercise.
KJF