From my understanding there is no straight forward way,
  but the following steps could help:

* Go to the queues overview in the Azure portal
* Enable dead-lettering on message expiration on your subscription/queue.
* Set TimeToLive on your message to say few seconds. 
//(I did while creating a test queue, in the creation it is simple)
* Push the message to your subscription.
* Within few seconds you will have all your messages in dead-letter queue.
//(Provided no app is reading from the subscription during those seconds)
*Finished