This is probably not exactly what you want, but it achieves the same desired result. Or at least, it's how I'm doing it. Login as admin of the portal. Then in the Admin->User Accounts page, on the bottom select Manage Profile Properties. Here you can add additional fields / edit existing fields / remove existing fields that will be on the user's profile. This only changes the fields on the user's profile page, not the registration page. Then you need to go back to User Accounts page and then select the User Settings on the bottom, and make sure that the check box for "Require a valid Profile for Registration" is checked. That way, when a new user registers, that user is required to fill out a profile, which includes the new fields that you have added. Hope this helps.