Doesn't exist. Shake isn't exactly a reliable method, even in my time with my old iPod touch, which used it for the undo function.
You're stuck using your button, don't worry about it too much. I don't think we have a reputation for bad buttons as of now.
I had many old Palm PDAs pass thorough my hands, some models had questionable quality power buttons, but none failed. So you should be OK, unless a defect rears its head or the phone is damaged.