How can I deploy to heroku with Google default credentials without the json file?

I'm looking to deploy a node app on heroku, and the key challenge i'm running into has to do with the Google default authorization workflow for Node. Google calls for downloading a json file with secret keys, and asks to use GOOGLE_APPLICATION_CREDENTIALS as the ENV Var name that points to the path of the json file. That is fine for local development, but in production I naturally do not want to upload the json file to source. Heroku allows for creating config vars, but each var is individual. Somehow I need to break up the json file into individual vars it would seem, but I don't know what to call them for Google to recognize them. There is a similar thread on this for Ruby -

How can I authorize a Google Service Account without the default credentials file?

but the equivalent does not work in Node.

any help would be much appreciated!

Thank you!

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