Sorry to bump this back to the top, but I haven't had any responses yet and am still confused as to how to properly deploy the code for a custom service task.
Using jBPM console to define processes with custom tasks - update the workitemdefinitions.conf to define the custom task attributes (icon, input, output parameters, ..)
Having a centralized server you may want to have a centralized configuration of the custom tasks. Be aware the executors (the jBPM console application) needs to be able to load the classes of the work item handlers (include into classpath).
The code snippet you've provided should be ok. assuming it works from the local context. So - when designing and running your instances from the jBPM console, and you configure the handlers globally, in the client side you don't need to configure anything else - the task name should be enough for the executor to find the correct handler (at least it works that way in jBPM6).
Have fun.. gabriel