adding extra parameters to the SSO auth cookie

Yes its possible. However you need to have a space for the setting to be created / copied on the Lithium side. You may need to create some small custom coding to retreive these values from the SSO object and have them stored into the custom profile / custom setting. It may also be done automatically... I can't recall. Either way you'll need to lodge a support ticket.  

Chris is correct, you should be able to add any user profile field -- like other fields in the sso token, use a pipe ("|") to delimit each setting and use <name>=<value> for the setting -- for example:

Li|..first parts of sso token go here...|login|email|profile.name_first=john|profile.name_last=doe|iL

great, thanks for the replies, I'll give it a go and post how it goes