Add new slugs via plugin?

Hello all,

I feel like this question has a simple answer, but after days of scouring the internet, the WordPress Codex, and plugin source files I still haven’t been able to uncover an answer.

What I want to do is add slugs to a WordPress installation at run time via a plugin, very much like how BuddyPress adds the members and activity slugs, with dynamic sub navigation within them like mysite.com/members/admin/ or incidentally wordpress.org/support/forum/hacks

What is the function or code to add these custom slugs to a WordPress installation via a plugin like that? I’ve searched everywhere and I can’t seem to find any information on this. Any advice would be greatly appreciated.. Thanks!