How can I archive unpublished comments?

Is there a way to archive unpublished comments? I am working on setting up a blog for a governmental entity. we are required to NOT delete comments that we elect no to publish (exception: spam). These unpublished comments must later be made available in the event of a publish disclosure request. It appears that there is no way to archive them, that the only way to keep them is to leave them in the Moderation Queue. The problem with this is that they will always show up at the top and be in the way. Does anyone know of a solution for this issue? Or another blog software that allows for keeping, but not deleting unpublished comments?