Joined: Jun 2010
Posts: 2,132
Likes: 1,522
From: Medford MA
Bikes: Ron Cooper touring, 1959 Jack Taylor 650b ladyback touring tandem, Vitus 979, Joe Bell painted Claud Butler Dalesman, Colin Laing curved tube tandem, heavily-Dilberted 1982 Trek 6xx, René Herse tandem
Adding to the dogpile here, my suggestion is to do the internal cable guide up proper-like, brazing in a stainless tube like Joe Bell does.
Doesn't exactly help the OP's predicament however. If I were Randy, I'd make a tight-fitting plug out of something plasticky and JB-Weld it in place. Then touch-up paint/blending/whatever.
__________________
Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.