Custom Alert Dialog Box (iOS 6 + 7)

I've made the (absolutely crazy) decision for my app, iComics to support iOS versions 5 through to 7. To ensure the app fits the design style of both 6/7, I'm currently re-engineering the app to feature a dynamic theming system that can configure the UI style depending on iOS version.
One component I'm working on right now is a custom version of the 'UIAlertView' popup box (As that one looks VASTLY different in iOS 7 now ^_^;). My goal for this control is to have it work exactly the same on both iOS 5/6 and 7, but to also dynamically change its appearance depending on the iOS version of the device.