... once posts get off the front few pages it's easy to overlook additions to them.
What Steve was probably referring to originally in repairing with additional paper is called "double-cutting".
Remove the thermostat, and fold the wires flat against the wall. Next, locate the pattern match for this area on your new material, and cut out an oversized piece of it to use for your repair. (2" extra to each side is good)
Make a hole in the repair piece in the right area to accomodate the wires, and place it over the repair area to assure you have a good pattern match. Lay the repair patch aside.
Moisten the wallpaper in the repair area with a sponge and warm water. Dampen the paper several times over about a 20 minute period.
Now, wet your repair patch if it's prepasted, or paste it just as you would for a new application. Push the wiring through the opening in the patch, and place the patch on the wall, directly over the existing paper.
Being careful to not let the patch slide as you work, use a stiff putty knife edge or other metal straightedge as a guide, and cut through both the patch, and the existing paper with a wallpaper knife, one side at a time outside of the missing paper area.
Now remove the patch, and using the tip of your knife to get a start, remove the existing paper inside your cut area. Once the area is free of paper, put some added paste on the area, and re-place the patch into the area. Smooth the patch working from the center outwards towards the new seam edges.
If this is done carefully, the pattern will match up nicely, and seams will be unobtrusive. To an extent, this works better with some papers than others, but it is a pretty universal method of repair.
Steve may see this new post and add his thoughts or variations, too.