Basically the trick is to have the heirlooms equiped and transmogged, and instead of putting them into your bag and mailing them, put them into your mail right from your character interface just like in the picture below: (Behold my epic paint skills)
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Here's proof that it works:
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Just imagine level 1 T6 warrior with Torch of the Damned walking around killing pigs... PRICELESS!
See the reactions of people as they see you in low level dungeons... PRICELESS!
Try it out, and post the result, so I can see what you did