As the owner of a Cannondale Synapse Carbon Fem 3 (you're right, it is cumbersome!)...I know exactly what you are referring to. When I bought my bike, inside the owner's packet was a couple of clear adhesive pads (stickers like pll posted) that you are to affix to those areas where the cables come into contact with the frame. Did you not get these adhesive pads with your bike? With the pads in place, I have not noticed any wear in this area.

Linda