Well for a start, you still have to use your custom Class::DBI module. The methods belonging to the stored objects are not stored in the CGI::Session wrapper, so you'll still have to load them the standard way, with use. And you ought to connect to the database, but I'm sure just using your module ought to do that for you.

I would think having the id for a row and the various classes knowing all of the details of what database and what table to use, should be enough to fetch the correct record from the database — even with so little info to go by.