Cast on stitches over the gap?

[peev]

Hello all. I'm knitting a scarf as a Christmas present, and am almost finished, but have come unstuck at the last hurdle. I'm knitting the Ribbed Keyhole Scarf and am at the point where the pattern says:

"Next row: Work ribbing for first 12 stitches, cast on 14 new stitches over the gap, join to stitches on other side of the gap and continue ribbing."

I have 12 stitches of rib on each needle - already knit on rhs, and am about to cast on the 14 stitches. However, I can't figure out how to do this. I assumed that I'd add them in front of the stitches on the left hand needle, then knit the whole lot onto the right needle. I tried that, and it left a loop of yarn across the stitches. I tried adding them at the end of the stitches I've already knitted on the right hand needle, but then the yarn is in the wrong place. I also tried casting on individual stitches and then passing them onto the left needle to be knit, but this doesn't work either.

Please help - once I've figured this out, I've only another 4 inches of ribbing to do. Many thanks in advance.