While we encourage all sponsor and referee letters to be submitted by the same deadline as your application, we will accept letters submitted after the deadline.
Ask all your sponsors to write one letter and have 1 of them submit it
Request (using our contact form) that an additional invitation be provided for your additional sponsors. You will need to supply the email addresses of any additional invitations you require. Once the invitations have been enabled--they will appear in your regular invitation screen once you login to the application system.