I can make it work by hacking XenForo_ControllerPublic_Index and duplicating the required code from XenForo_ControllerPublic_Online but I'm a little lost on how to do this properly with a plugin.
After setting up an event listener do I simply create a new actionIndex() function that would have the bits of code I need or do I need to duplicate more. I saw the link for adding new actions ( http://xenforo.com/community/threads/how-to-add-more-actions-to-an-existing-controller.11202/ ) but I'm curious what you need to do for already existing actions.
On a side note is there a detailed discussion of the inner workings of the Plugin system? I see myself doing more plugins and having a better grasp on the technology would probably be a good time.