Convert existing iOS paid app to freemium model with in-app purchase

Question

Hi,

I currently have a paid app in the store. Apple have not allowed a 'lite' version to be submitted as well, so I have no choice but to update the current paid version to a freemium (with in app purchase) model. I have the problem of not loosing functionality for v1 users that have purchased the app the first time round.

Is there any way to determine if an application have been updated from a previously installed version so I can unlock the paid parts of the app?

Two similar questions (from a few months ago):

http://stackoverflow.com/questions/1575965/transition-an-existing-paid-for-app-to-free-version-with-in-app-purchase

http://stackoverflow.com/questions/2219868/iphone-upgrade-existing-paid-application-on-app-store-to-free-application-with