[bobbyh]

Nick, are you talking about something like this?

* https://bbpress.org/forums/topic/plugin-add-sidebar

This doesn’t do any magic integration with WordPress, it just lets you put a sidebar.php file in your theme directory that can be invoked from multiple pages. I actually ended not using this approach (despite writing the plugin). Instead, I just added some PHP/xhtml at the end of header.php.