What you are describing is the primary reason I switched from the NHibernate persistence to the SQL Persistence. You have so much more flexibility.
I use a common schema for all NServiceBus persistence named… you guessed it NServiceBus
You can prefix the table names for the endpoint.
options.TablePrefix(FormattableString.Invariant($"{nameParts[0]}{nameParts[1]}"));
So If You have an endpoint named “Notification.Server”, it’s persistence tables would all be “nservicebus.notification_server_xxx”. This would be true for outbox, timeout, and sagas. It makes it very easy to distinguish between them and keeps everything in the same schema location for ease of lookup, etc.