1.  Make everything as a membership in Nanacast

2.  Make a membership group in Nanacast and add your free and paid memberships to the group

3.  Set up both memberships in Nanacast to point to the same memberlock installation

4.  Add your content to each membership from within Nanacast 

Clients will signup via the free membership.  A client record will be created on the blog.  The blog will "fetch" the content from Nanacast that is specific to that client, based on their membership.  If they upgrade, a new record is created on Nanacast and the old one is cancelled.  The new RSS feed is set to your blog for that client, which contains the info for the paid content.