When you hit Customize > Forms & Views and select the form you are using, which sounds like create_user, you will see a Duplicate button. Duplicate the form and edit the new one as you please. Add, remove, or edit any fields you want. Then if you go to your Operator Profile, there is a button at the bottom of the form, "Override the application’s forms and views". Click that and find your form (New Visitor Account) and select the override. You may need to log in again for it to take affect.
Visible If is a JavaScript expression, but the sponsor profile is not readily available within the browser.