Use the iFi ieMatch. I wrote a review on it a few weeks ago. If you click on the review link under my name it should be one of the more recent ones.
http://www.head-fi.org/products/ifi-audio-iematch-headphone-travel-accessory/reviews/17505
http://www.head-fi.org/products/ifi-audio-iematch-headphone-travel-accessory/reviews/17505