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!
you are probably aware , super forks are a bit ify at the bottom of the steering stem a good stopper may aggravate this condition .some supers have a mod to the stem I think Roger M has done some of them. Regards D F .
OK. You can let the single cable come out of the hole in the bars, from the inverted lever, and then feed it to a separate “whiffletree” pivotted bar, fixed either on the bars or fork crown, with two cables, one to each brake, from there down to the brake plates. If you Google “whiffletree” you will see that it is a proper engineering term !
I got one for a 350 Ducati single that I’m restoring off ebay for £30 and its new. You can get cheaper ones, Menani do one which is bulkier and in a plastic housing. I have one like this I’m happy to sell if its of use to someone very cheap.