Repeat Steps 3-4 until you reach a corner, then work one I-cord row as follows: k3, then keep repeating Steps 3-4 to the next corner.
Continue seaming both pieces together with the I-cord until you reach the beginning of the I-cord. Break yarn, and pull tail-end trough remaining 3 sts.
Use tail to seam the end of the i-cord to the beginning, to give the impression of an uninterrupted.