Cast on at the end of a row?

I’ve started ‘Edgar’ from Knitty tonight ( ) because I need a smallish scarf to wear with my plush-collared jacket.

Here’s the line that gives me trouble: “Row 18: Sl1, k5, sl1, k2tog, psso, k6, CO 9 sts. 22 sts.”

How do I cast on extra stitches at the end of a row (presumably using the yarn you’re already knitting with)?
I usually cast on with the long tail method, but that clearly isn’t going to work here…