Now I think I'm entitled to say I can cable without a needle. I had to go to Preston for a training course today - that's 1 hour and 10 minutes knitting each way. Should I take a needle? No, let's pack a crotchet hook and see what happens. You know what? I didn't drop a single stitch. I can now officially cable without a needle.
What's made the difference is holding the stitch. With yarn this smooth, the stitches just weren't staying in place, they unravelled pretty much every time. What I do now is pull them off the needle, hold them in my fingers, work the other stitches and pop them back on the needle. It felt awkward at first, because I had to work the other stitches with my hands in an odd position, but it's coming easily now and it's wonderful - quicker than using a needle, not so frustrating as leaving the stitch to drop.
I finally worked up courage to put a tape measure over the back - it's a bit bigger than 42". I'm knitting the 42" size and, although the pattern doesn't give you a schematic (which I hate! Why not tell me exactly how many inches that piece should measure?) I think the bit extra will be the ease so I'm hoping it will fit.