@Stef: You are my hero!

I went out,and bought a Harken block and 2m of depower rope (18€). I just untied the handle at the end, put in the harken block using 2 bowline knots and after some trimming, ready to race.
And what a difference it makes, so easy to hold the position
Like A Koch says : its critical to have

dumb question - what does this 4:1 give you?
Is it a mechanical advantage on the depower trim line making it easier to pull down?

Yup. So that you can use the trim strap to trim the kite instead of moving the bar. When youre riding the raceboard and a gust hits you pull the 4:1 trim instead of letting the bar out which would mess up your body position/weight placement.

Plus the trim is mechanically easier and you get a better fine tuning , it's easier to make small adjustments.