BuddyPress.org

Here’s a method for creating a sort of BP frame that takes the admin bar and footer of your BP installation and wraps it around another arbitrary web page on your server. You could use this, for instance, to bring the BP admin bar into MediaWiki or something like that.

http://teleogistic.net/2009/10/displaying-the-buddypress-admin-bar-in-other-applications/

The basic idea is that a bare-bones WP page (footer only, including the admin bar) gets loaded in the background, which contains the user’s logged-in state.