Setting up secrets without direct access to files

I'm using Portainer on my server.
In Generate API Keys section (https://supabase.com/docs/guides/hosting/docker#generate-api-keys) it's said that you need to replace anon and service keys in

volumes/api/kong.yml

volumes/api/kong.yml

, however I can't really do that.
In Portainer, you can create a stack using

docker-compose.yml

docker-compose.yml

, but you can't load files directly for a stack (ie.

volumes/api/kong.yml

volumes/api/kong.yml

).
Any suggestions?

How to configure and deploy Supabase.