Set current menu item based on post tags

I’d like to tweak my navigation menu so that the current-menu-item class is applied to a particular menu item based on tags added to the current post.

In other words, when I am viewing a single post, I want to trigger menu item ‘foo’ to appear active if tag ‘bar’ is applied to the post.

I’m pretty sure this is possible via adding the right code to my functions.php, I just can’t figure out how.

This is on my child theme to Scherzo, on WP 3.3.2.