Head-tube cable stops are one of the stupidest things ever put on a bike. Only a few misguided builders are still putting them on some road bikes, but many bikes are still in use from the period when they were the height of fashion. They replace the minor problem of cable rub with the massively worse problem of tortured cable housing leading to premature failure.
Housings in head tube cable stops bend abruptly when the rider swings the handlebars further than a few degrees to either side. This can happen in low-speed tight turns or when stuffing the bike into small spaces, like the back of a hatchback or a small SUV. The book has nothing to say about this. Obedient mechanics just keep replacing housings and sending riders back out to develop shifting problems.
The new bars on the Serotta have internal cable routing like the old ones did, but the housing exits from the aero extension a little farther from the head tube now. The way the bars are shaped at the outer end, the housing HAS to run inside and go out through the hole provided.
The other shop had tried a sweeping curve, but still had a tight kink at the stop. I fiddled with different lengths and angles for an hour or so until I had a brainstorm.
The junction ferrules on brake noodles are drilled for brake cables, which are fatter than shift cables. To insure that the linear-wire shift housing wouldn't push through the junction ferrules I replaced them with junction ferrules designed for shift housing. It was a little tricky feeding the plastic liner of the noodle through the smaller drilling of the new ferrule, but it eventually fit.
To make the installation less conspicuous I put shrink tubing on the noodles.
Noodles probably wouldn't help with older STI levers on drop bars, but now that everyone is routing their cables under the tape the housings exit closer to the headset. That means the cables come in more vertically, which would probably feed into the noodles successfully.
I will be conducting more experiments. I doubt that they will end up in the book.