I think I had a twinkle on the above post--but now here's the real deal from Elizabeth Zimmerman herself:
She's describing short row shaping to make the back longer. I'll just quote her here and you can adapt it to your pattern:
Work across the back to within 3 stitches of the underarm seam-stitch. Wrap the wool around the next (unworked) stitch on the lefthand needle (she describes how to wrap her which I'm sure you know)
Turn. Purl back to within 3 stitches of the other underarm seam-stitch and repeat for second wrap. turn and continue around.
Now: When you come to the wrapped stitch, work IT and the WRAP together.
Continue around, and treat the second wrapped stitch as follows: Slip the wrap, knit the stitch, pass the wrap over, (or SSK). The back is now 2 rows longer than the front. Repeat at regular intervals as often as wished.