How to add taxonomy to Users menu in admin?

I want to create a taxonomy that is related to the users, therefore I'd like to show the taxonomy under "Users" menu within wordpress admin. In codex there's a mention that you can attach taxonomy to "nav_menu_item" but I can't find any working example of how this works. If I use:

register_taxonomy( 'expertise', array( 'nav_menu_item' ), $args );

or

register_taxonomy( 'expertise', array( 'users' ), $args );

it doesn't work.

Any help would be much appreciated.