One method would be to create a system variable to be used as the template.
MSH|^~\&|sender|sender|recipient|recipient|{SYSTEM_DATE[yyyyMMddhhmmss]}||MDM^T02|{UUID-NO-DASHES}|P|2.3|||NE|NE
EVN|T02|{SYSTEM_DATE[yyyyMMddhhmmss]}
PID|1||123||FakeLastName^FakeFirstName^^||19500101000000|M|||||||||||111551234|||
TXA|1|CM|TX|20130127142151||||20130127142151||||{UUID-NO-DASHES}||994|||AU|UC|AV|||^^^^^^^^^^^^^^20130127142151
OBX|1|ST|||Discharge|||||||||20130127142151
Then create a custom mapping function that creates your HL7 message and sets the value to the above template.
message = qie.createHL7Message();
message.setNode('/', qie.evaluateTemplate(qie.getVariable('templateHL7')));