How the heck do you guys do it? There is a front cable stop, then just a small horizontal tube right behind the seatpost.

This is the best pic I can find of a similar (but larger) frame than mine (a 12″).
Hoping to run a XTR M900 cantilever on the back, is there a curved cable insert that I am missing? Or should I just run some plastic cable straw material over the whole run, terminating after that weird stop on the seat tube?
Thanks,
Ryan