Nonunique Display Names

I've got a request from my client for an intranet site that will allow users in the company to post questions to a board for members of the IT staff to answer. The requirement is that the non-IT staff users need to be semi-anonymous.

I'll define semi-anonymous as follows: unique login, email, etc. Hidden profiles, no direct messaging, etc. Nonunique display name. So how it should look is a user logs in with their unique username / password, but their display name is "board_user" or something similar.

But there's an anonymous login, you might say. This won't work in this case because the compliance department here needs to be able to audit the messages posted to the board. So though a comment shows anonymous to the board, it is in actuality tied to a unique user ID and can be audited as such.

Now, I can manually edit the database to change people's display name (and display_l_name? and display_seo_name?) to be "board_user". But I would like this to be automatic. Ideally I would like there to be an option in the AdminCP to have display names be non-unique.

I understand why this is an unusual request as for normal cases you want people to identify each other. But for me, for this install, I need most of the users to be anonymous.

If you can think of another way to do this, I welcome your ideas.