Dudley, I have done what your asking several times. I found the biggest problem depends on the exit as it leaves the wingtip. I sometimes ca the new one to the old one and use the old one as a pull string. This works if the eyelet at the wingtip is large enough. As said above you can glue it directly to the side of the old one. I've even had to butt join them with ca which is a bit more riskier as it could fall off leaving the existing cable in the wing. In the event that happens, I use small music wire and carefully fish it into the bellcrank area. Once the cable is there which is usually easier than the termination part. I then carefully use crimp tubes while others use wrapping. Ken