Thanks for theadvice, using the Service Task was easier than I expected.
Following the instructions in the example worked. Just a little bit of extra config was required to get the "Service Task" added to the "KnowledgeSession" in "Spring".
e.g. Spring Config
<
bean id="jboss.jbpm.serviceTaskHandler" class="org.jbpm.bpmn2.handler.ServiceTaskHandler" />
<
bean id="jboss.jbpm.knowledgeSession1.workItemManager" factory-bean="jboss.jbpm.knowledgeSession1" factory-method="getWorkItemManager"/>
<
bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
<property name="targetObject" ref="jboss.jbpm.knowledgeSession1.workItemManager"/>
<property name="targetMethod" value="registerWorkItemHandler"/>
<property name="arguments">
<list>
<value>Service Task</value>
<ref bean="jboss.jbpm.serviceTaskHandler"/>
</list>
</property>
</bean>