Just found this:
https://github.com/albhm/macPPM
Which is the equivalent of Smartpropoplus for OS X according to the developer.
(Smartpropolus is a method for connecting your transmitter directly to your Windows computer using a 3.5mm mono audio cable)
Haven't tried it myself though, I don't own a Mac. Seems like it might require some hacking skills. It would be interesting to hear if anybody has tried it.