Gateway Service annotations - valuelist default value

I have a datafield Country on a custom entity Customer. I have added the valuelist annotation to that field and made it fixed-values which all appears to work. However, when I create a new customer, I want the country to default to 'US'. Is there a way to set the default value in the DEFINE method of the MPC_EXT class or do I have to extend the Object Page of my List Report Fiori Elements application to set the default country?