Here's how I have it setup on mine; I used mildly modified V-brake braided 'noodle' added to the length of the correct cable for the handlepost I have - in this case an 'S' type. The noodle allows for a tighter angle of attack for the cable coming in to the bottom of the caliper and I've had no problems with rubbing once I fitted this. My front cable also runs to a lever on the left of the bars which admittedly is a non-standard thing to do but it also seemed to help - if you are up for making the polar leap of swapping brake handles (my Brompton has no rear brake and it's good in the UK to have left for the front so you can signal right at junctions and brake at the same time)