Welcome to the Octopus community!
Thanks for your question.
Could you give me more information about why the “Deploy config map as raw YAML” step will not work for you?
One way to achieve this is to package the config map as a build artifact and use that in your Octopus release.
When a change to the file is pushed to the code repository, this triggers a build, and the build can trigger the creation of an Octopus release with the new package. Alternatively, the build can push the package to Octopus, with this triggering a release and deployment. The documentation for this can be found here: https://octopus.com/docs/projects/project-triggers/automatic-release-creation
You can scope the config map to use if, for example, the files are specific to an environment.