I took a look at the plugin you linked to as an example. Seems like that would actually require more work than adding a normal link. Since you need to define a list of keywords and their links.
Giving this more thought it would be possible to query a list of names from the directory and then search the post content for those names and then add links doing this on a post save event. As long as the directory has a max of a couple hundred entries that should work just fine scaling beyond that would require some form of background processing of a post. That too is doable but much more complicated to develop. I’ve added this to my list of ideas for extensions.