Can the JMSPriority be updated for messages on the ESB?

I really would like to be able to change the JMSPriority for the following scenario:

A messaging-partner sends all its messages (of various types) to the same queue in Sonic. On this queue an ESB process grabs the messages and routes them to the message-type/partner specific on-ramp queue. As some messages of some messageTypes are content/reply type I want to give these messages a higher priority, so that they are processed before the one-way-sent messages.

However it seems the JMSPriority cannot be changed for messages in the ESB.

I've tried:

• Transformation service using Javascript === results in ===> runtime error
• Transformation service using  XSLT === results in ===> runtime error
• Custom Java service in an ESB process, which changes the JMSPriority header property === results in ===> no runtime error, but JMSPriority remains 4
• Custom Java service in an ESB process, which creates a new message object with the changed JMSPriority === results in ===> no runtime error, but JMSPriority remains 4

As far as I could comprehend the JMS specifications an option to update the JMSPriority is optional to be implemented...

Is it at all possible to update the JMSPriority for messages that reside on the ESB?