Wanted to share my approach to this. It’s not as amazing as I want ( mostly due to needing to press a button in the editor to generate / re-generate the links ), but it works pretty well and our world builders are AMPed to not have to place these things automatically.
I made a C++ class that extends NavLinkProxy. Then exposed an event to the Editor as a button, when clicked, it gathers all the nav in the world and executes an algorithm to place Nav Links on any edges that aren’t shared with other Nav Mesh Polys.
I was worried I would never find a solution to this, but then this came together in a day or two only. 
Still has some iteration to do but happy with the result so far!:
