Will it be ugly? Why not introduce a interface or interceptor that can be put in the properties, and let the user deal with this. You did it with the database per tenant why not here. The user of hibernate is then in control to implement this.

Something like:

String getTableName(String tableNameByHibernate);

The things I expect from hibernate that this is save in every code path for instance in query caches.

And adding this tenant solution, will make the tenant solution of hibernate more complete.