Why is it not what you need? Sounds like you have the setup (go from point a to point b, using this node graph, avoiding these obstacles), and you have the docs describing the algorithm...

You might be able to do something that I thought about when playing with some A Star code that a guy had online a few years ago. He had a speed test for his code that generated a bunch of random paths between random start/end points on a particular map (like 500) and I noticed (since he had a visual of the paths as they were generated) that many of the random paths when thru the same points frequently. Somehow you could analyze and extract good points which had a high frequency of being reused to select your set of Nav points (a Monty Carlo method....)

Another method moght be randomly picking points and growing rectangles that have clear edges (stoping that edges growth when it hits an obstacle) and then using the centers of the resulting rectangles as you Nav points. You would have to do several cysle to fill in missed parts of the map (or another pattern using lines and/or growing diamonds/diagonal rectangles....)