fork wiring has been done.....buy an awol to customize, or source a fork:

The New 2016 Specialized AWOL Touring Bikes - CyclingAbout CyclingAbout

"...The AWOL Evo comes with a few features that make this bike totally awesome. My favourite feature without doubt is the dynamo light-to-USB-charger switch, which is integrated into the barend plug (image by Cycling-Ex.com). That is a collaboration piece made by Supernova for their E3 lights and The Plug III USB charger – it’s unfortunately not available aftermarket. All dynamo cable wiring is internal in the fork which is super clean...."

"....If you’re thinking of doing a custom build with an internal geared hub, this could be a great frameset option given how versatile the swinger dropouts make the bike. At US $700, it’s a bit of a steal for a Rohloff/belt compatible touring frame with all the braze-ons....."

modifiying existing frame? should be possible within limits.
internal smaller tube not always essential. some builders
(as when i bought my mercian) just have in/out nozzles
brazed onto the tubing for cable housing to pass through.

any reason you don't want the rear light wire to exit
the frame higher up the seatstay?