How to create multiple persistent data at doc level ?

How to create multiple persistent data at doc level (designmap.xml) instaed of object level as created in "PersistentList" sdk sample plugin. Tell , what changes we need to do in "PersistentList" sample Plugin to achieve persistent data at document level. I have ssen "basicpersistinterface" plugin but unable to understand how we can do it in "persistentList" plugin