I've been searching for a roof rack for my 2015 Hardtop (not S) ever since I got the car in October 2014!
Mini says something is coming (that doesn't require rails) but no ETA
Thule says they're testing the fit now and to check back in about 30 days
Yakima seems to have one that works (according to their fit guide: Q TOWERS 4 PACK SYSTEM).
I'm hoping Thule comes out with one since I have a lot of accessories already.
I'll be a bit hacked off if Mini come out with something, since we were told at launch that you needed roof rail to fit any kind of bars, so I duly changed my order which caused a whole world of grief. And I still haven't bought bars yet, possibly never will