Exception Handling in Service Layer which can propagated into Flex plugin-layer

Hello,

In my current plugin I'm using 3rd party  CIM- client libraries which throw exceptions for transaction which are invalid. I want to process these exceptions and bubble these into Flex Layer . Is there a mechanism to do this ? Any pointer regarding this would be useful

Also if we decide on adding custom Error- Codes ,what is the best approach to propagate this into Flex layer.

Thanks,