Hello,
Yes a service task is the way to go.
In order to create a custom (domain specific) service task you need to do what is described below,
http://community.jboss.org/people/bpmn2user/blog/2011/03/28/jbpm5--work-itemdomain-specific-process-hello-process-example
If you want to use your work item handler with the gwt-server and the console ( or your own console that uses the server) you can register the work item handler (instead of step 5 of the instruction of the above link) within the CustomWorkItemHandlers.conf located inside gwt-console-server's META-INF directory (also mentioned nicely in http://community.jboss.org/people/bpmn2user/blog/2011/03/30/jbpm5-example--human-task-forms-with-variables--workitems).
p.s. i'm not sure about this, that's what i've done, in order not to (possibly) lose the functionality of log and email in step 1 of the first link (jbpm5--work-itemdomain-specific-process-hello-process-example) you could add to the CustomWorkItem.conf the configuration for log and email as well (as found in drools-core-xxxx.jar -> META-INF/WorkDefinitions.conf), i.e.
import org.drools.process.core.datatype.impl.type.ObjectDataType;
import org.drools.process.core.datatype.impl.type.StringDataType;
[
[
"name" : "Email",
"parameters" : [
"From" : new StringDataType(),
"To" : new StringDataType(),
"Subject" : new StringDataType(),
"Body" : new StringDataType()
],
"displayName" : "Email",
"icon" : "icons/import_statement.gif",
"customEditor" : "org.drools.eclipse.flow.common.editor.editpart.work.EmailCustomEditor"
],
[
"name" : "Log",
"parameters" : [
"Message" : new StringDataType()
],
"displayName" : "Log",
"icon" : "icons/open.gif",
"customEditor" : "org.drools.eclipse.flow.common.editor.editpart.work.SampleCustomEditor"
],
[
"name" : "HelloProcessExtension",
"icon" : "icons/action.gif",
"displayName" : "HelloProcessExtension"
]
]