Here is What you could do. If there is anything wrong with the phone at all like camera blurry or bad battery life or like a bad pixel (you can check by saving a black picture on your phone turing the brightness up all the way and go to that black picture) you can trade it in and they will give you another iPhone 5 from white box and it will have a clean esn.
And Apple isn't going to noticed that it is not activated?
There is no way that this would ever work.