Go to the Medical Schools section of the application and click the Edit link next to the school you to which you wish to assign letters.
Scroll to the bottom of the page and click Continue.
Select the letter(s) you would like to assign to that school.
If you have previously submitted your application, go to the Main Menu and click Submit Application in order to save your changes. This will not cause processing delays or charge you additional fees.
Ok I know its technically part of the primary AMCAS application, but you don't need it done until your secondaries right?
So regarding OP's question we can't add LOR requests without a fee?