I would try to fine a plain neoprene grommet (round type with groove around the outer circumference) that fits acceptably in the oval hole, with flanges engaged all around. Good source would be www.mcmaster.com , but a good hardware store may carry a selection large enough too. Then put in a cable housing, either waxed like the dickens or wrapped with the thinnest tape you can find, sticky side out. Then install these in the tube, and fill the space between grommet and housing with silicone sealant. Sculpt to the best of your ability and let cure. If you have any little bits sticking up, you can shave them off with a single-edged razor blade after cure.