schema proxying virtual database

Dear List,

There are many opensource applications that support postgresql
(eg , gforge , bricolage , dspam ..) but does not use schemas(namespaces)
as a result of which you are forced to use/create a new database and loose
the
advantage of linking the application data with your existing database.
as no-cross database queries can be done in PG.

my question is , is it a feasible idea to have some special kind of database
in the postgresql cluster that mimics a schema of an existsing database.

say rt3 is a special database that links to existing maindb databases'
rt3 namespace then any DDL / DML done to public schema of rt3 database
is redirected to rt3 namespace of the existing database maindb's rt3 schema.

regds
mallah.