Yes, that did it :)
{code:xml}
<scriptTask id="_2" name="Hello" >
<script>
System.out.println("### Starting Greetings process ###");
org.drools.runtime.process.WorkflowProcessInstance process = (org.drools.runtime.process.WorkflowProcessInstance)kcontext.getProcessInstance();
kcontext.getKnowledgeRuntime().insert(process);
System.out.println("### Inserted process instance ###");
</script>
</scriptTask>
{code}
But it is stil a bit of a hack... it would be nice to be able to "prepare" the process before starting it or even having the process instance inserted automatically.