Installing mechanical group set on "electronic only" frame
I have a solution for you (if you haven't got the electronic groupset already), inspired by road bikes from '70s and '80s era. 

Namely, the rear brake cable on the top tube. 


on some of those bikes runs through the large eyelets through a very lengthy outer cable (the eyelets merely hold the cable in place):



while on others there are two cable stops near the ends of the top tube and the inner cable is visible:






Now, if you do the same with your derailleur cables, namely run them through lengthy outer cables, the force required for shifting is in fact exerted only near the brifter and the derailleur itself, thus places prepared for clamping.

The only question is whether the outer cable stiffness (in length) is high enough to assure shifting accuracy.


  I don't own the pictures, they are purely for illustration.