You only need to get the plugs through the holes.
Use extra long cables and route them all out the top of the seat tube, plug them in, then drop the junction B down.
This is my plan what I hope to do and then the junction box will probably end up sitting above where the top bottle boss enters the frame. Thanks for the answer on the SD300 cables!
@SoYaap started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
You only need to get the plugs through the holes.
Use extra long cables and route them all out the top of the seat tube, plug them in, then drop the junction B down.