As it currently stands it appears that it is not available (here):
no free In-App Purchases are available
But Apple is going to implement this feature for developers with iOS7! (source1, source2)
I am sure that there are better documentation in the member center but I am currently locked out waiting for my boss to approve a new license agreement. This is a wonderful idea besides just the metadata reasons. It would allow the developer to offer free in-app purchases for special offers or periods of time too.