How to design history storage

We are using Camunda workflow to model our business scenario. How can we design history backend such that all history related to live instances remain in the main storage but the history related to the completed instances are stored/moved to the custom immutable storage. We do not want to write custom query layer. We have a way to wrap our custom database to look like main database so history queries would work fine. But how do we proceed with storage/moving of selected history events?