On my way to enrich my jumping technique and considering that my Vegas 9 has limited hangtime potential, I am thinking of starting to use the stopper ball in order to free a hand or two during flight. Any advice on how to do that? Do I pull it down before the jump, as I am building up speed? Do I pull it down at the initial pulling of the bar right at the beggining of the jump? Any help appreciated, thanks!

Doesn't North use Microloop/hook option for that?

Moving the stopper around before or during jumping is affecting jumping technique and or limiting your jumping acrobatics or whatever you do.. never worked for me, I liked the microhook when I rode North's
You can ride like you used to and for a deadman or whatever you simply hook in during takeoff and you have your hands free..

The times I have used the stopper are for attempting a deadman and I pulled it in as close to take off aas possible. What you need to be aware of is that when you land you sheet in to get a soft landing but you probably use the sheeting and depower range to ride off with control - if you don't have a push away stopper then get ready to land with much more power than normal. This made for a quite a few faceplants and superman style splashdowns

Now if I'm doing a board-off I generally hold the bar in with one hand close to or straddling the centreline - give a bit more control and if you have to ditchthe borad or are goign to land badly then you can regain control quicker.

I have never used one but I would consider a micro-loop quite dodgy on smaller kites - even on my 11m C kite I could see how a microloop could get you in the shit - they are maybe the domain of bigger kites lighter winds?