I don't know if this will help, since you've already started, but when I use a double strand of the same yarn, I pull from the center and the outside of the same ball. If you're using wool, you could just break one strand of yarn, find the outside end of the yarn you didn't break, and attach it using spit-splice method.
Or maybe you could put both balls IN the bag you're knitting.... then there wouldn't be any long strands hanging down that would twist. :??