Came looking for advice, left with the reassurance that comes with realizing that your plan isn't any jankier than anybody else's setup. I mount my light on the front of a porteur rack, so the cable has lots of area where it's just supported by air. Thinking that in those sections I might try enclosing the rear light and dynamo output wires together in heat-shrink with a 1/32" piece of TIG rod so that there's some support.

My usual excuse for messy dyno wiring is that the wiring on my bike is temporary. OTOH, some of my temporary wiring has been on a bike for 10 years. Once I get my travel bike painted I may actually try to do a permanent wiring job. I have provisions for most wires to travel in the frame/fork.

I prefer to think of my dyno wiring as a theft deterrent. Would you want to be caught riding a bike like mine, with the wires wrapped around the fork and everything?