You're correct, there is no API to define in app purchase identifiers dynamically. One other thing, which you should check with App Review, I get the impression that only those in app purchase identifiers that are defined at the time of the formal app review, are approved for use for in app purchase use once the app is in production.
I now proceed, but please understand, I could be wrong on any or all of the following - please tread carefully -
There might be a creative use of non-renewingsubscription identifiers, where a number of non-renewing subscription identifiers are defined ahead of time, but without associated content. The app could maintain contact with a server process to know what identifiers are active and what the associated content it's assigned with. However, all identifiers would have to be associated with a predefined price initially. With all this, I'm sure that there are other issues to be handled regarding the in app purchase process.
There is also the potentially larger issue - what is the content to be sold?
rich kubota - rkubota@apple.com
developer technical support CoreOS/Hardware/MFI