I see you have the right general idea. Let me see if I can tell you what the book says.
You do your temporary cast on with enough sitches for the cable and at least 1 maybe 2 would be better to have in Rev St st to flank the cable.
If you laid the piece you have out flat in a rectangle let's call the part on the right the front shoulder (just to help me) and the end on the left the back shoulder. (I think I'm thinking of this right, if not, it is the other way. )
Hold the needle with the newly cast on stitches on it in your right hand, (the working yarn is coming from here), and the front shoulder needle in your left hand (drop the back shoulder needle for now).
Making sure the right side is facing you knit the first st from the left needle and past the last cast on st over it. Turn your work so that you can work the first row from the WS.
Row 1 (WS): (you want to knit the stitches that will be Rev St st and Purl your cable stitches) Sl 1 st purlwise with the yarn in front, work across your little row until you have one stitch on the cable needle section, purl that stitch together with the first stitch on the back shoulder needle (make sure the WS of it is facing you as you do this) (Note: when you purl those two stitches together you are working with two needles be sure the one holding your hat stitches is the needle in front and the cable needle is the back needle as you purl the 2tog) Turn again.
Now the pieces are joined.
Row 2 is a RS row: Slip the first stitch purlwise with the yarn in back, work across until you have 1 stitch on the cable needle part and work a SSK using the last stitch there as the first Slip and the first stitch on the hat needle as the 2nd one. Turn.
Repeat rows 1 and 2 crossing cables as you need to. Joining this way will make a decorative line of stitches on each side of the cable, but it looks good.
Let me know if this works for you. Good luck.