Hmmm, Leslie. Not sure exactly what official technique I'm using to graft. I guess I've done enough duplicate stitch and backstitch seams in the last few months that I feel comfortable just seeing what needs to be done. In some ways it's just like grafting shoulder seams together. Certainly the one row (from the sweater) looks just like that.
So here's what I did. Start by going into to the first live stitch from above. Then bring needle under one whole stitch in the sweater (that's an upside down "v") and pull yarn through, leaving a tail to weave in later. Now you can start working back and forth, stitch by stitch, from top/live stitches to bottom/sweater stitches. When going into the live stitches, take needle down into the left half of the previous stitch and up into the right half of the next stitch. Then move to the bottom row (under the next upside down "v") and up to the live stitches again. The sides are just sewn in with mattress stitch of course.
And that's it.