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It can be done with a T47 BB shell and a 30mm crank spindle if you use the right BB. The last bike I built has a T47 shell with the Di2 cables and rear brake hose running through it, and a Wheels Manufacturing external bearing T47 BB.
If you wanted to use BSA68 cups, then you would indeed need a custom BB shell, with at least a 50mm OD and then rather deep steps for the BB threads.
So the only option for completely internal routing in the BB shell with enough room would actually be a custom machined shell? But would also depend on where the chainstay is attached to the shell to not interfere with the bearing threads.
Slow day here at work, might draw it out on CAD.