This is how you do it:
After you pass a hurdle, you press space (or mouse) 1 time at normal speed, then you press twice fast. (speed varies depending on incoming hurdle's hight).
If hurdles are at same hight, you can press mouse (or space) at equal speed.
You approach the hurdles from below.
That it it, rest all about practice and patience.
I scored about 100 but have not made SSs and won't play it more.)