While I suspect there's probably a cleaner, more maintainable way to achieve what you want, you should be able to manipulate the order windows appear using the windowLevel
property - although to be honest the last time I tried to do this was on iOS 5 so maybe that's changed. But generally you'd do something like:
windowToPlaceInFront.windowLevel = windowToPutInBack.windowLevel + 1.0f;