Does the pattern tell you to do a crochet edging?
I just looked at the pattern (call it a miracle--I found my copy of the magazine!). So that edging on the front doesn't carry around to the back? That's kind of dumb.
I have an idea, but I'm not sure how you'd attach at the shoulder edge. I guess you could just sew it.
You could do an applied i-cord. It would kind of match the edging on the front. Pick up stitches across the back on a circular needle. Knit 3 stitches and slide them back onto the left tip. Then knit 2, k2tog. Put these back on the left tip. Keep going across, k2, k2tog and putting them back. You'll get a nice little icord on the edge of your knitting. You'll have to play with how to attach them at the shoulder edge, though.