Hey Cobra, your post piqued my interest. I like little challenges like this so I decided to try and find a way to avoid damage on level 10. I succeeded.
Firstly, at 4:34 in the video you linked, the trick is to activate force speed (I did this with four stars, I would imagine it could be done with less though) and basically run a half circle around the downward slope. The idea is to keep your speed up by running the circle while pushing slightly against the slope in order to slow your descent, kind of like a marble rolling around a cone. Remember to run diagonally since diagonal movement is faster than forwards movement. It's tricky and may take a few dozen attempts to actually get down with no damage whatsoever, but you should find if you try this that you can get down with under 10 damage fairly easily and then just work from there and try to tweak it and keep trying until you get down completely unscathed.
As for 4:50, here the solution is much easier. Wait for the probe droid outside to start entering the vent, then jump such that you crash into the probe droid instead of the ceiling. Collisions with probe droids (and probably other flying enemies, not sure though) will stop you but won't cause any damage.