It is not directly possible.
Guvnor uses JCR (Jackrabbit or Modeshape).
Whilst these can be configured to persist to a database the schema and content is proprietary and not easily queried. From Jackrabbit's JavaDocs:-
"SimpleDbPersistenceManager is a generic JDBC-based PersistenceManager for Jackrabbit that persists...objects using a simple custom binary serialization format... and a very basic non-normalized database schema (in essence tables with one 'key' and one 'data' column)."
Other people have asked the same question and I have given suggestions as to how a solution might still be available.
Please search the mailing list and have a dig around.