Currently there is a filter (OpenidConsumerSessionFilter) that looks at (all?) requests and sees if there is a request parameter containing the User's OpenID. The User's OpenID is then stored in the Session to be used later on for the OpenID login at this consumer.

I would think just having the User sent directly to the OpenID long page with the attribute in the URL string might be better and then let other more appropriate classes assign the OpenID to the session.