I don`t think there is a way at the BladeLogic level to block the extended object data to be grabbed by the ETL. It only means you have to delete the data from the BladeLogic OM database before running ETL.
Your best bet is to limit the data by running specific properties file during the ETL run.
Question: What is the purpose you are limiting the extended object data from being pulled over?
customer has large amount of extended objects that they have but not all of them they need to have sent over to BSARA.