Cross database foreign key workaround?

List,
    What are the recommended work arounds for cross database foreign keys?
As I understand it transactions are not atomic with the TCL method.  I have
a situation that requires a master database and then a separate database for
every subscriber.  Subscribers need read/write to both databases.  I chose
separate databases because there are 20+ large tables that would require
uid/gid columns, indexes and where conditions to separate information by
subscriber.  I thought that was too much overhead.  Should I just use my
application to make changes and ensure references that need to take place
across databases?  Or should I add a uid/gid to all necessary tables, create
indexes and update all necessary where clauses?  Ideas?

/B