I've run it two ways.

The first was using the cable routing braze-ons left over from the thumb shifters on the mountain bike frame (see photo below).
The tricky bit there was in the rear, going from the frame into the hub.
The cable stop is intended to have housing going to a derailleur (that's good).
The cable stop is over the chain stay (that's bad).
The distance from the cable stop to the hub is very short - only about 2-3" (that's bad).
An S-shaped bend was needed but it was a fairly tight pair of bends.
The resulting friction slowed the response of the gear changing mechanism.
It worked but I was always looking for something better.

The current set up is as you describe - uninterrupted cable housing from the thumb shifter to the hub, held in place using zip ties. It is inelegant and still has a lot of friction in the system.