First of all I have to excuse for the maybe misleading question: I read that it's not possible, so the question actually is: Is this true and if yes, is there another possibility to accomplish this relation-behavior? But let's describe my situation:
I'm developing a small SharePoint 2010 solution and am not sure how to deploy some relations. I want to deploy everything with only the help of packages and features, that means I cannot use the SharePoint UI. That's what I want to do:
I'm designing several content types, e.g. Report and Entry. I'm using XML-Definitions to design them. Then I build list definitions that describe that e.g. the ReportList handles items of the type Report. And now I'm stuck: I want to declare that every Entry belongs to one Report. Therefore I'm adding a lookup field to the definition of the content type for Entry, but lookup fields need list instances when I deploy their content types.
I would like to declare the relation without a need of these instances. Users should have the ability to decide which lists they want to add for themselves. Is there a best practice for declaring such relation without having list instances?