Since the characteristics of the charger are specified, all Apple needs to have is an adapter or cable that uses the necessary resistance ratios to identify the charger characteristics. At worst, the only change needed to the iPhone itself would be a software change.
To demonstrate this, review this video, wherein an iPhone is charged happily and without complaining from a laboratory power supply once the proper resistor ratios are placed between the USB pins.
I suspected something like that. Thanks for the information.