Here's what you need.
http://www.sheldonbrown.com/harris/c...tml#centerpull
NEW! CAH59 Fork Crown Housing Stop $14.95 Each
This unit allows you to use traditional cantilevers or center-pull cantilevers without a housing stop on the headset. It is designed to bolt onto the front of the fork crown. This can solve a number of problems, and can improve cable routing by letting the cable get around even a low handlebar stem without a sharp kink.
This is not intended for use with suspension forks. It may be possible to make it work with some suspension forks by mounting it on the upside-down "U" bridge that connects the legs, but it must not be mounted on the fork crown of a suspsension fork as it will cause unpredictable brake application as the fork responds to bumps.
Good luck-- I have this housing stop on the rear brake bridge of my bike-- It works frount or back. It can, however move sideways and cause your brakes to fail, so keep it straight and the bolt tight!
Good luck.