Curling cables nearly annoyed me to death!!! What a nerve-wracking way to try to knit!
Later, when I got my Knit Pick Options, that problem went away. But in the meantime, there I was trying to knit socks with this horribly looping cable. And to finish my project I had to use what I had on hand. So..... I read about the value of boiling water!
I put a small pot of water on the stove and when it came up to the boil I plunked my cable down in the bubbling water and swished it around. Don't put the part that connects to the needles into the water, just most of the cable.
I kept taking them out and re-plunging them in until I could feel a difference in the coil of the cable. It wasn't a perfect (or a permanent) solution but it got me through the project. When the coil started to tighten again after a couple hours knitting I just cranked up the water pot and put the cable back in its "hot tub"!
Hope this helps!