According to this portion (see red), we can add the letters of recommendations after we've submitted. I'm hoping someone else can elaborate as how the schools that app was sent to initially will be able to view the updates.
"Once your application is e-submitted, your application is locked and most sections cannot be updated for the remainder of the application cycle. The only sections which can be updated are:
Edit Contact Information
Edit Profile Information (username, password, security question, etc.)
Add DO programs to apply to whose deadlines have not yet passed
Edit or delete a evaluations whose status remains INCOMPLETE;add new evaluations up to the limit of six. Please note that COMPLETE evaluations cannot be changed.
ADD NEW but CANNOT EDIT or DELETE test scores, experiences, achievements and certifications.
If you have any updates which need to be made to other sections of your application, you must submit these updates directly to your DO programs."