How to setup a Service Integration Bus to send an MQRFH2 back through WebSphere MQ

The only mechanism available to cause a bus destination to automatically add an RFH2 header containing the JMS message properties is the _MQRFH2Allowed context property on the destination (which defaults to the context property on the foreign bus if no foreign/alias destinations are configured).                                          
                                                                   
With this in mind, one option might be to configure an alias destination with a similar name to the real WMQ Destination.           
                                                                   
This would require customization of the destination returned from getReplyTo to choose the right alias, using the com.ibm.websphere.sib.api.jms package. Here is an example of how you might build a SIBus queue object from the JMSReplyTo field:                                                  
JmsQueue replyToQueue = JmsFactoryFactory.newInstance().createQueue(msg.getReplyTo().toString()); 

The methods of the JmsQueue interface are described here: JmsQueue Interface                                         
If the range of queue names is large, then configuring a second foreign bus might be a better option, setting different destination defaults on the two foreign buses (one with _MQRFH2Allowed=true and the other with _MQRFH2Allowed=false). This would avoid defining any alias destinations, and mean just changing the bus name on the replyToQueue as appropriate.