OdaDataSetHandle ref for existing .rptdesign template

Starting with a .rptdesign template I am looking to manipulate this at runtime to run against a number of databases.

http://dev.eclipse.org/newslists/news.eclipse.birt/msg20490.html
outlines doing
OdaDataSetHandle dsHandle = designFactory.newOdaDataSet( "ds",
                                "org.eclipse.birt.report.data.oda.jdbc.JdbcSelectDataSet" );
I could then point odaURL to the new database, using:
                dsHandle.setProperty( "odaURL", "jdbc:classicmodels:sampledb" );

My question is how can I get an instance of OdaDataSetHandle for existing .rptdesign rather than create a new one?