Attempting to install inside existing Docker Composed environment

I have an existing tech stack of several frontend (angular, react) and backend (Nginx, Python Django, with Redis & Postgresql) and now we want to test DF. In order to conserve resources I do not want to use the Bitnami image because apache, mysql and another redis would be a redundant waste of memory, but the Install documentation and Github install doesn’t appear to have configuration options to use Postgresql from the start.

The docs say:

If you want to change from one system database to another after you’ve already run setup/installation:

Is there any way to add DF to my existing docker-compose and point it to my existing Postgres and Redis containers?