I'm painting an 81 Raleigh Team Pro (Reynolds 753) with a rusted bottom bracket shell. The Cinelli shell originally had grooves to guide the cables. With the rust and time, the cables have worn all the way through the shell, so there's a thin hole about 1/2" long.

My thought is to add a plastic cable guide and just put it over the holes. Would this work? Do the holes need to be filled?