Join association across two databases with :through


I'm trying to join two tables that are in different databases. I
tried using :through but I'm getting complaints about trying to span
databases. I've also tried find_by_sql and just plopped the SQL into
the function but I get complaints about one user not being able to
access the other database. I know I could just make both databases
accessible by the same username/password pair but, besides being
hacky, I don't have control of the databases.

Thanks for any help you can give me on this,