Knit the sock carrying the yarn in back. When you get to the point where the sock will be folded either
1) move the yarns to the front and carry them up the front (same as carrying them in the back) or
2) turn the sock inside out (pull it through your needles), moving the yarns to what is now the "back" and knit to the end from there. Since it is ribbing it is easy to knit from either side as you will always k the k and p the p.