Then one day recently I discovered a solution while browsing the Techniques section of knitty.com. An article by Theresa Vinson Stenersen on "Casting On" says:
Another good way to avoid this problem is by using two balls of yarn -- or both ends of the same ball of yarn -- joined at the slip knot. Just cast on one extra stitch and unknot the slip knot when you're finished casting on.Why didn't I ever think of that??? It seems so obvious when somebody points it out! I don't even know why I was reading the article, since I have done a long-tail cast on since my grandmother first taught me how to knit, but I will never do it another way if I have to cast on more than about 30 stitches. Thank you, Theresa.