You won't be able to do it only with changing properties, you need to update the code as well. As a general hint I would suggest to turn on verbose logging on Converter services (instructions how to change the logging level can be found at VMware KB: Increasing the logging levels to verbose for vCenter Converter application components). Then you can try to run the conversion with the settings you want through GUI and then look at the log files (Converter Server log) and see how job spec was populated. It can be used as a reference for your code then.
HTH