keeping with the electrical tape tip….
Don, a member here had me install cable guides on his 1939 beautiful Holdsworth. The stress of not scratching was great.

I placed electrical tape next to where I wanted the guides to go, so I wouldn't scratch the frame as when the guides are expanded to go over it, then slide them to their final position.

In your case, I like the Velo Orange (on sale now, $4 a set) which come flat and use the electrical tape on the inside, trim with a razor blade.