I had to read your post a few times, Charles, to get into my mind what you were explaining. What you're describing is a really good idea, unfortunately I don't have the straight edges you're describing. Or a top mounted bearing bit. I think there's a saying about wishes and horses.
I like your method, Charles, as it's simple to setup and no extra cutting to make a jig. Plus, if I understand your method correctly, I don't have to allow for the distance between the bit and a guide bushing when making a jig; something I like.
Because the wood I'll be using for the two wall hanging shelves is oak, and I'm not hurring through this project, I think I look into getting the straight edges and top mounted bearing bit. I know the problems I've had just cutting the dadoes in the prototype and I'd perfer not to have them when making the two wall hanging shelves with the oak.
Occasionally looking back will help you avoid hitting those thing you will hit if you constantly look back.