[Exim] Querying two MySQL-Servers after another

Hello,
if a mysql lookup is successful but does not return any data because
the SQL statement did not match anything in the database, is it
possible to try the lookup again on the second server in mysq_servers
before failing the lookup? The reason for this is we have two databases
of user-data which we want both to be able to use authenticated SMTP on
our Mail-server but we want to keep them in separate databases.

Thank You,
    Florian Wallner