Step 1: Start by setting your rearview mirror as you normally would.
Then, lean your head all the way to the left so it touches the driver's window. From that position, set your left side-view mirror so you can see the back corner of your car. Now lean the same distance the other way, and set your right side-view mirror the same way.
Now, here's what happens. When a car comes up behind you, you should first see it in your rearview mirror. But as it passes you (let's say on your left), you'll see it move to the left side of your rearview mirror. And as its left headlight disappears from your rearview mirror, it should instantly show up in your left side-view mirror. There should be no delay. It should slip from one to the other, so you can always see it.