Getting a frame built ?, have the right fork tip made to accept this end of the axle contact system
and use that hub which is the only one that mates with it.

http://www.nabendynamo.de/produkte/s...kerlos_en.html

http://www.nabendynamo.de/produkte/p...tahlgabeln.pdf
http://www.nabendynamo.de/produkte/p...gabel%2010.pdf

as you see the wire goes inside the fork blade. you can have the fork crown and steerer drilled
then the wire exits down thru the bottom of the steerer tube. and direct to the fork crown mounted headlight ..

hiding the wire back to the taillight is a separate issue. I expect your builder can sort it out,
particularly if they braze the rear rack on the frame, then rack tubes can run the wire though them..

in theory the foil inside SKS mudguards can be a conductor , the Set Koga fitted on my WTR
has grommets that should function as contacts.
but having a conversation with a NL builder, the reliabolity of that scheme is not aas good as just running a Wire..
I have hot melt glued wire inside the mudguards , before.. so it stays on the tire side till it exits near what was a mudguard mounted taillight..
so then you have the downtube to run the wire thru and back out behind the BB shell

my own stuff is not that sophisticated, now ,
I run the wire down the gear cable to the R'off Shift box
then up a rack and mudguard strut..

my bike friday I fitted the taillight so it is right behind the bottom rear of the seat mast
bottle cage..