How to discard messages from queue?

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Java

We have an application that reads 4MB messages from an IBM Websphere queue (version 7.5) using JMS. Under certain circumstances, I want to discard messages from the queue without reading them. I am trying to figure out if there is a way to do this programatically without reading the entire 4MB message, which takes several seconds (there could be hundreds of messages that need to be discarded). In the absense of a discard() method (or similar), here is what I have tried:

BytesMessage msg = (BytesMessage)queueReceiver.receiveNoWait();
bytesRead = msg.readBytes(msgBytes, 1024); // just read 1024 bytes
queueReceiver.close();

The above code is no quicker than retrieving the entire 4MB message from the queue (by reading into a larger buffer). This leads me to believe that the receiveNoWait() call is downloading the entire message into an internal buffer before the readBytes() call is made. The only other information I can provide is that the queue is set to "auto acknowledge" when the session is started:

queueSession = queueConnection.createQueueSession(false, QueueSession.AUTO_ACKNOWLEDGE);

If I were to change this to CLIENT_ACKNOWLEDGE and acknowlege the message using msg.acknowledge(), would that have the desired effect?

Thanks for any help,
Doug