You can run the rear brake line out of the holes on either side of the frame near the headtube. I have my rear brake line coming out of the right hand side of the frame, then looping round to the brake lever on the left of the handle bars.Just noticed that the rear brake cable runs down the left hand side so its going to have to do a tight loop round to the brake lever (UK - rear brake on left). Hoping the bike shop does a nice tidy job due to cable OCD lol.
I have all my cables (rear brake, dropper post and motor remote control) coming out of the hole in the right of the frame