She would ask if you were game, to be honest before seeing her I too had never heard of or experienced a handstand bj.
It ends up being very similar to the women laying prone on end of the bed while the guy stands at the edge and goes into the oral skull-banging. Just this gives her an opportunity to control the depth control and she was a bit more typical smaller Asian but also its something novel that she can keep her regulars with. I have never had any other providers offer it, and while I enjoyed it, and would repeat; I also don't think it needs to be done with everyone.
The dynamics if one were to try and repeat.
She would start in the 69 position on the massage table and then do a kick-over to handstand, then use her one leg to assist in the balance and lining up (using the side wall - reducing the shaking arms) and then proceed to do multiple handstand push-ups only depth control was how strong she was in going down. She was able to do this far longer than I would think a person would be able to maintain, I thought it would have been a 20-30 second thing, but she kept at it for 2-3 minutes (not a vigorous speed, but enough to be impressed by her strength and stamina)