Just do the same as on a Brum Scott, with a twin-pull front brake lever. The bit pulling on the two cables has to be free to pivot in the middle so as to equalise the pull on each cable. Some of the big Enfield twins, Constellation, Interceptor, etc., had twin front brakes like the Brum Scott, with an identical twin-pull lever, so you might be able to get one from an Enfield twin parts supplier, such as Burton Bike Bits.
The other way to do it is with a Vincent-style scissor-action gizmo mounted on the forks, but that would be a LOT more complicated, and not very elegant on a two-speed Scott!
Brian