I am a fairly experienced knitter, but have not, until now, encountered a pattern that required me to cast on stitches after I had worked the piece for some length. Specifically, my pattern is a baby wrap that is worked in one piece. After several inches on the back, I have to cast on a number of new stitches at the beginning of six rows (for the sleeves). How do I do that? I usually cast on with the double cast on (long tail) method, but obviously, that won't work now that I am in the middle of the piece. Any advice is appreciated.