You can use methods to by-pass or flow through the driver to execute an untranslated query directly on a single source. In the UnityStatement class are these two methods:

ResultSet executeByPassQuery(String dbName, String sql) 
int executeByPassUpdate(String dbName, String sql) 

These methods will execute a query or update on a single source (given by name). The SQL statement provided is not parsed or validated and passed directly to the source driver. There is no overhead in this type of query as it is equivalent to invoking the source's JDBC driver directly.