Depending upon how tight the curve of the stem is, you can usually safely splice in a section 6 to 12" long shaping it out of a straight board. The splice repair shown in the book does work but its not as good as it could be.
The attached photos kind of show how I now do most of my stem splices. The red coloring is just to make it easier to see the laminate that is used to reinforce the relatively short splice that is used on the stem. Its all glued together and makes a very strong repair . If you feather the edge of the laminate, match the grain of the old stem, and stain the color to match, the repair is extremely hard to see.