Schubert, Right-way Audio marketed these some years ago. They look like insulators that you see on telephone poles, but not made of glass. I cannot find any such firm now. I bought 24 of them.
I had never heard of one per cable either until I was urged to try it by the Right-way owner. Sometimes I just cannot achieve this but consistently I have found it best.
Geoffkait, I have never tried fishing cords from ceiling eye hooks. Perhaps this is because my ceilings are 11 feet up and also because it looks so crappy. I have used cord from tripods left over from my photography days. For some reason, perhaps vibrations, I prefer isolators.