I'd probably think of a strategy of persistance outside the bean
itself. For example, having the bean generate an XML file with the name
of the user (any way you can ensure it is uniquely identifiable with
every visit). This way, when the user logs in, you read the file and
reistate persistent data. As they modify or submit their data set, you
save it.

Remember Java has a means of converting objects directly to XML. The
class is smart enough to handle collections as well, and can be
restored in a snap.
Also, you can use session objects, and figure out a way of backing them
up to file (uniquely identifiable by user) when they are done or when
the session expires.

In my experience, I use unique GUIDs for users, and use these
identifiers to track user activities on my sites.