I am assuming you are wanting something to come back as a SOAP fault element?
Unhandled process exceptions are sent back as faults. So, theoretically, you could write a service component to do nothing but throw an exception. Then you could route your process to call that in specific situations.
As an alternative, I would consider having something like an additional 'status' output variable that always came back in the response which indicated the status of your process.
Good Luck,
Ryan M. Jacobs
rjacobs@cardinalsolution.com
Cardinal Solutions Group