How do you use python-decouple to load a .env file outside the expected paths?

I figured it out.

Instead of importing decouple.config and doing the usual config('FOOBAR'), create a new decouple.Config object using RepositoryEnv('/path/to/env-file').

from decouple import Config, RepositoryEnv

DOTENV_FILE = '/opt/envs/my-project/.env'
env_config = Config(RepositoryEnv(DOTENV_FILE))

# use the Config().get() method as you normally would since 
# decouple.config uses that internally. 
# i.e. config('SECRET_KEY') = env_config.get('SECRET_KEY')
SECRET_KEY = env_config.get('SECRET_KEY')

Hopefully this helps someone.