This little contraption, called the Boompro by V-MODA should be able to help you out:
http://v-moda.com/boompro-microphone/
It is like the mod mic, except it actually hooks into the 3.5mm jack on headphones that have detachable cables. The only thing is it might not fit in headphones that have special locking mechanisms..And I'm not sure if the M50x has such a mechanism.
Have any of you M50x users tried the Boompro with your cans?
Yeah the M50x has locking mechanism and a 2.5mm input so it makes it hard to find anything that matches up.
Another guy found a solution, though it may look tidy with the way he did it.