Last week one of my teammates was doing handstands against the wall on a bosu ball for rehab. I thought it was sweet and tried doing it freestanding. As soon as I got on, the ball and I started to bounce pretty violently up and down. I discovered that the way I push in a handstand is like a pulsation. Each small push corrects for the time that I'm not pushing. After a few tries it started to level out and the bouncing stopped. I've done 2x30sec HS on it a couple days now and have noticed a huge difference in the stability of my freestanding HS. I've also noticed that my forearms are incredibly tired after just 30sec.
Just thought I'd share with fellow HS enthusiasts.
Lemme know if anyone tries it or has done it before.