I run the cables for the rear brake and derailleur through the guide that clamps to the bottom of the boom. The front brake cable did not fit with those two, so also used a cable tie on handlebar to keep it out of the way. A portion of the front brake cable is tucked into the front edge of the cable clamp.
My picture isn't very good, but you can buy cable guides that bolt onto bottle cage bosses. This one keeps my brake cables secure and out of the way, and keeps the look clean. A couple of cable ties between the bottle boss and the steerer tube does the rest.