deploy on Heroku a docker image (with volumes), without having source code

I need to deploy on Heroku a Docker image I have from a public registry. Such image needs some params to be run, including a certificate file. Locally, I can use docker compose specifying in the docker-compose.yml file all the env vars and volumes.

# === docker-compose.yml ===
services:
  my_service:
    image: public.images.repo/my-service
    container_name: my_service
    volumes:
      - /Users/me/public.pem:/public.pem
    environment:
      - CERT_PATH=/public.pem

Unfortunately, I've just seen that Heroku doesn't support docker compose.

I see that is supports the heroku.yml file, but it requires to have the Dockerfile, that I don't have and can't modify since I only have the image. And, apparently, there is no volume field.

# === heroku.yml ===
build:
  docker:
    web: Dockerfile
    worker: worker/Dockerfile
release:
  image: worker

How can I deploy a docker container, with volumes to import certificate files?