I would advise you to use CGI::Session. This way you would be able to store an arbitrary complicated data into the session object and the cookie would only need to contain the session id to restore that information.
This is a good suggestion - but the front end (which is SSI powered) may not have access to the datastore that would be used. I expect this is the case here.
This would explain the somewhat arcane format that the OP is getting at with the values in the cookie.
--tidiness is the memory loss of environmental mnemonics