AutoParkour is a mod that allows you to select any block and makes the jump to that block for you!
The current version requires you to sneak to the back of the block you are standing on, and is not completely reliable. I am currently in school, so will only be working on this on and off, so it might take a while for any updates.
I am still working on this, but I've had exams and such so haven't had much time. At the moment this does exactly what you describe if you select a four block jump. It does a jump to give you the necessary speed and then jumps on the very last possible second. This is not the very last moment, because most parkour anti-cheats negate overly accurate timing. And this is completely client sided so no packet changes.
I see. Makes sense I guess for it to do it by itself. The thing is though I am not yet able to detect when you are at the end of a block. For the same reason a triple neo is very hard to program since you need to be perfectly on the edge of the block when you jump. I am working on this though, hopefully block edge detection will work. That is mainly what I am trying to fix and then I should be able to put up a download link.