Managing whether it is an iPhone 4 or 5 is not a ton of work, it really only makes a difference when you initialize the button and that is it.
You can do this by getting the screen size using the following code
CGRect screenBounds = [[UIScreen mainScreen] bounds];
if (screenBounds.height == 568) {
// This is an iPhone 5
} else if (screenBounds.height == 480) {
// This is an iPhone 4S or below
} else {
// Some other device, maybe an iPad?
}
Then just add the button in that way, pretty straightforward