Objectiv-C works by sending a message to an object. If that object responds to the message, it does something. The message is essentially just a string and in fact you can use strings to build selectors.
Normally, these private API selectors would show up in a class dump and Apple will reject you app. But, if you're clever, you can hide them from a class dump. You could encrypt the strings, then decrypt them at runtime and Apple could no longer find your private API usage in a static scan.
At runtime they could detect you calling private APIs, but it would be easy enough to code it so that you don't call any private APIs for a few days after first launch or make them so they're turned on with a server side flag. That way Apple would never notice the private api usage during an App Store review.
Normally, these private API selectors would show up in a class dump and Apple will reject you app. But, if you're clever, you can hide them from a class dump. You could encrypt the strings, then decrypt them at runtime and Apple could no longer find your private API usage in a static scan.
At runtime they could detect you calling private APIs, but it would be easy enough to code it so that you don't call any private APIs for a few days after first launch or make them so they're turned on with a server side flag. That way Apple would never notice the private api usage during an App Store review.