Zen Menu Logic allows the user to select any of several custom menus to appear on a per page basis.
This plugin only works under the following conditions: 1. the theme has registered at least one menu location 2. user has created at least one custom menu with one or more menu items. 3. user has selected which menu location the plugin should work on in the Settings -> Zen Menu Logic options page
If those 3 conditions are met, then the edit page for every page and post and custom post type will contain a meta box listing the custom menus with radio buttons. All you need do is select which custom menu should display when that page is called.