We have a similar feature with our Canon iR copiers, called Department ID Management. The section where the user can enter their ID/pwd is under a menu item called Special Features. However, you cannot manually make the feature appear. It is not something you can tick via the printer queue 'Options & Supplies' tab. Instead, the queue needs to be correctly configured in order for the Canon driver software to communicate with the printer to determine that the feature is enabled. Maybe you have a similar feature?
I downloaded the KM C250 105.pkg a couple of weeks ago for another postee. I don't have it with me here at home, but I remember there being two folders that were copied to the KM folder (in ./Library/Printers/). One was a filters folder and the other was the PDEs folder, which contains the plugins for the extended features provided by a driver. It is possible that the pane that lets you enter your account info will be located in this folder. I can check this when I get back to work.
PaHu