Hold work parallel to each other on two needles with right sides facing each other. With a third needle and using the yarn that is still attached to your work, knit through the first stitches on both needles at the same time. Work the next set of sts the same way. Bind off the first st. Continue across the row until all the sts have been worked. Break yarn and pull through.
This technique will leave a seam, but it will be a strong join and is quick and easy to do.