I really cant see why this job is not straightforward if you have access to the right di2 wire lengths, and assuming the cable can be routed through the entirety of the handlebar between hoods. Might be some flimsy leftover stuff in there, but you can almost certainly guide it through the bar.
This was my thought, but the mechanics used to work with pro scene so I can gather he does things by the books and sometimes it's hard for them to think outside the box.
Should be a lot simpler than in the video since most of the Di2 is connected in the handlebar instead and only one wire is going into the frame, last TT bike repair I got had same brakes, 2 junctions behind the stem and 8 cables going inside the cockpit, now that was an ordeal.
I really cant see why this job is not straightforward if you have access to the right di2 wire lengths, and assuming the cable can be routed through the entirety of the handlebar between hoods. Might be some flimsy leftover stuff in there, but you can almost certainly guide it through the bar.