The process was pretty easy. Good instructions from Threads, as always. It requires precision to look good, but isn't complicated. One trial run was enough for me to be confident I can do it on the shirt.
I considered making up a tutorial about this, but I guess I have doubts about the ethics of making a tutorial from published and copyrighted material. But, not everyone does. A quick search turned up this tutorial - generally the same method I used.
Right side, placket closed:
The placket looks like it is curving out to the left in the pic, but IRL it isn't.
Wrong side (sorry for the blurry picture):
This isn't the fabric I'll be using for the shirt. But wouldn't that be fun if it was...