What you want is not possible. iOS displays the name of the app under the icon, nothing else. If you want the name of the app to be more than the max displayable characters (indicated as 12 by Craig), you will have to deal with truncation.
It is worth noting, however, that the name that shows in the iTunes Store is not the application name. You set that in iTunes Connect. As far as I am aware, the name of the app only shows up in a handful of places, most of the time under the same truncation rules as under the icon. It'll show in iTunes (not the store, but after it is downloaded), in the "Usages" section of the device, and in the device search. Really, if you want your entire app name to fit under the icon and can get it to fit in 12 characters, you should have no issues whatsoever.