How to create multiple persistent data in document level using "PersistentList" sample plug-in?

I want to create multiple document based persistent objects using the "PersistentList" plug-in. I have tried "BasicPersistInterface" sample plug-in, but it only lets you create a single persistent object. I followed this solution but I am not able to return multiple persistent members that I added to the persistent interface defintion. "PersistentList" sample plug-in  lets you create multiple persistent objects but only at object level. Is there a way to create those multiple objects in document level?