I'm sorry, I don't understand the question - you need a secondary data source connection that shows all the lists and libraries? If so, you might want to try the Lists web service in SharePoint - http://msdn.microsoft.com/en-us/library/lists.lists.getlistcollection(v=office.12).aspx. I just tried a data connection to GetListCollection. Unfortunately, it doesn't generate a schema in IP, so you'd likely need some code to return the data to an XML file in the form that you could use for a drop down.
If you are using ShP / IP 2010, there may be a way to get these using a REST data connection.