Any standard BMX/MTB calliper brake should fit with the 451 rim. What you have to do is swap the barrel adjuster and the anchor bolt around, in a similar manner to most lady's step-through frame bicycles. You can route it from the top as per normal - you will just need a couple of zip-ties to hold the cable in place when it bends down to be routed through the cable holders (You could also use a 135-degree noodle meant for V-brakes)