I can prepare a standalone function that can return true/false for a current user and a forum, but it can’t do anything else, and you would need to write your own handling to load templates and every thing else. That doesn’t exists right now, because no one asked before because it would be too much work to handle outside of the plugin, and since it will deal with theme templates I will not be able to assist in any way.
Now, I have on the list for the next version of the plugin to include such function.