Here is the link
to a video and instructions at Annie's Attic. Instead of working into a chain, or previous row of crochet, you would simply crochet into the knitted stitches or ends of the rows.
The advantage of crocheting is that you don't need to attach it or join it really in the same way you would with knitting. Depending on the construction of your sweater, you may be able to start the border right where you last bound off, and not have to worry about joining a new strand. If you have any questions or whatnot, just holler!!!