Env Variable in .ebextensions "files:" section

I defined an environment variable called MY_ENVIRONMENT_VARIABLE in AWS Elastic Beanstalk's Software Configuration tab.

Now I would like to use this environment variable in the "files:" section of a .ebextensions config file.

Resources:
  AWSEBAutoScalingGroup:
    Metadata:
      AWS::CloudFormation::Authentication:
        S3Auth:
          type: S3
          buckets: arn:aws:s3:::SomeS3Bucket
          roleName: aws-elasticbeanstalk-ec2-role

files:
  "/tmp/application.properties" :
    mode: "000644"
    owner: root
    group: root
    source: { "Ref" : "MY_ENVIRONMENT_VARIABLE" }
    authentication: S3Auth

container_commands:
  01-apply-configuration:
    command: mv /tmp/application.properties .

It seems to be possible to reference environment variables in the "container_commands:" section (by using bash scripts) but I couldn't find any references that it is possible inside the "files:" section.

Does anybody have an example of how to use environment variables inside the "files:" section?