Di2 11 speed on rim brake steel frame: clever/stupid/goofy solutions?

[benadrian]

I recently bought a mechanical brake Di2 11 speed group from Clean39t. I've never owned or used Di2 before. My intention was to see if I liked it, but also I knew I'd have some kind of fun challenge and project to fit it on to my rim brake, steel frame road bike.

Before I did anything irreversible to the frame, I wanted to try out the Di2. So I came up with this craziness. I took a Gatorade bottle and put a small hole in the bottom. I placed this bottle in the seat tube bottle cage. I put the battery and B junction in the bottle. I then ran the FD, RD, and main wires to junction A tightly along the frame and zip-tied them down. I was able to tuck any excess wire into the seat tube bottle. Ugly, yeah, but it went smoothly

So yeah, Ultegra Di2 and kicks the pants off of my mechanical 105. So now, how do I do a more permanent installation?

This is a classic steel frame. There's no oversized shaping or tubing in which t stuff shifting electronics. There are vent holes in the BB to the down tube, seat tube, and chain stays. Annoyingly, there's no way the 4 port B junction will fit through a vent hole in the BB. I'm pretty sure there's enough room to fit wires around the BB sleeve though, and enough room to get the di2 cables into the seat tube, downtube, and chain stay. So, I have a few options.

As Internal As Possible
I could probably fit the junction box in the seat tube. Then I'd have to drill a downtube hole, a seat tube hole, and enlarge the chainstay vent hole. That would be some crazy routing for a steel frame, but the most elegant if I pull it off.

Internal Battery
Get one of the external mounted 4 port, under BB junction boxes. Drill one hole on the bottom of the BB to run to the seat tube battery, then do very nice and secure external cable routing.

Nicer External Routing
Find a case or bag like I'm doing with the water bottle, but mount it in a slick way under the downtube or in the down tube/seat tube junction area. No drilling, just route as cleverly as possible.

Abandon this crazy idea
Flip the Di2 and go withe Wheeltop (no real support), Force AXS (expensive, will need a new freehub body, cranks, BB, etc), get the nicest Ultegra/Dura Ace mechanical everything that I can find? Give up on my steel frame road bike idea?

Thoughts?