Okay. How about this?
Instead of using a special “Anonymous Mode” like is currently done, just add a checkmark by posts. When this checkmark is active, the post has a state (isAnonymous) set to true.
When someone else views the topic, it is shown as simply “Anonymous.” (Post username is set to anonymous?) Admins will see the same thing, but will be able to press a button to send a server request to get the true user. This, of course, should be logged.
The initial poster will still see it as his own post (maybe with an Anon tag or something) and will still be able to edit/modify/whatever the post.
This way, there’s no user needed and it’s just cleaner overall.