Interesting! Thanks guys. I think I'm just going to go with the simpler solution of under the BB routing. I'll have to drill and tap a hole, but that's no big deal really.
Frame is an 82 Trek of Ishiwata 022 tubing. Originally for 27" wheels, but with 700c wheels and mid reach brakes easily clears some nice wide rubber.
Maybe I'll change the title and document the whole process here so others can follow along with my process.
Here's a shot of the generous tire clearance
