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Plastic sleeve, then di2 Park tool cable thing inside, done.
If the plastic sleeve is not doing it then brake cable first to guide the sleeve or resort to magnet.
Whatever you do you need to plan beforehand how to route all the bullshit in the easiest way possible. Guide several cables in one if possible, get the Di2 before the hydro hoses, etc.
I do this all the time unfortunately, feel free to ask if it gets horrible.
I used to use a combination of thread, wires, spokes, welding wire magnets and spoke nipples. These days I mostly use the Park magnetic kit for internal routing.