BuddyPress.org

I must admit that I all the template redirection of BP and WP are somewhat magical and mysterious to me.

What about just requiring the template? If you’re using the BP Group Extension API, you need to have a display() method; the content of the method could be to require the necessary template file. That’s what the BuddyPress Group Wiki plugin does.

It’s helpful to look at a few plugins that have robust templating for their display: Group Wiki, Group Documents, and Group Blog all do it differently, but maybe they’ll point you in the right direction.