Expanding primary links on node pages

I have seen variants on this question in many places, but haven't yet seen a solution to my specific question.

In my primary links, let's say I have a top level category of "News" and then a second level category called "Local News" that is a child. So if I click "News" in the top navigation, only then does "Local News" get revealed as a second level menu item. The organization of my navigation mirrors the organization of my categories (taxonomy).

That functionality is working fine for me. What I can't figure out is this: if I am viewing a story that has the taxonomy classification of "Local News" how can I have the second-level navigation item of "Local News" appear when I am on the page for the full story node? Any node page that I browse to only shows the first level of my primary links.

It seems that the problem is how to have the node communicate with the primary links to tell it what menu item should be the active one, and then to display any second level links under that category.

This situation obviously becomes complicated if the story is given taxonomy terms that fall under different top level categories in the navigation.

So maybe I'm looking for functionality that is irrational. Regardless, any direction on this problem would be much appreciated.