conditional authentication

We are looking at providing a backup service to users if and only if
their primary service is down. Our regular users authentication is based
on query against a Mysql DB. Is it possible to setup a second group of
users, (under a different realm perhaps) to auth against two different
databases? One Database is to check the credentials, the other is to
tell us if their service is up, neither database is the same db we use
for our normal users.
-- 
Kenny Dail <[email protected]>