Just to update this thread, I ended up just creating a separate DB for archived entities.
This is a clunky solution because you need to manually convert entities to the archived DB and then delete the original entity. This also might possibly breaks some long-term report types, although you might be able to join the entities from the two DBs.
But it does have the added benefit that the archived entities are completely separate in search and selection fields. Also has the benefit that you can have extra fields for the archived entities without polluting the regular entity fields.