Since DJ 2.0.4, JasperReports writing JRXML feature is enabled and can be used for later design retouching (in iReport maybe)
Once you have your design ready, use any of these:
String xmlData = DynamicJasperHelper.generateJRXML(dr, new ClassicLayoutManager(), parameters, "UTF-8");
or
DynamicJasperHelper.generateJRXML(dr, new ClassicLayoutManager() , parameters, "UTF-8", outputStream);
or
DynamicJasperHelper.generateJRXML(dr, new ClassicLayoutManager() , parameters, "UTF-8", destinationFilePath);
NOTE: Some exported designs that will fail when loading later because they may need some objects to be present in the parameters map.