With the wrong side of each knitted piece facing out, and the needles parallel, slip a third (working) needle into the first stitch on each of the two needles.
Wrap yarn around working needle as if to knit, and pull a loop through. Allow the first stitch from each of the parallel needles to fall from the needles.
*Knit together the new first stitch on both parallel needles in the same way as above.
There will be two stitches on the working needle.
Using one of the two parallel needles, pass the first stitch on the working needle over the second stitch and off the needle as you normally would when binding off.
Repeat from * until only one stitch remains on the working needle.
Break yarn and pull the tail through the last stitch to fasten off.
PS: Whenever given the option between a 3-Needle Bind Off or Kitchener Stitch, I usually choose Kitchener. It's a slightly more elegant method of grafting live stitches. For a tutorial, click HERE.