How to use Hydra with MariaDB

I want to set up a Hydra CI on my server, but my main database server is MariaDB, and I can’t afford to migrate everything to Postgres. If I understand things correctly, it is possible to override the hydra package to add DBDMariaDB or DBDmysql to its environment, but I can’t seem to find how to apply said override.

How can I override hydra-unstable to add the MariaDB DBD backend, if at all possible?

Would be news to me. Can’t you just run multiple database servers?