How do I use oci-containers "imageFile"?

Alternate title: “How do I use an image that I saved to disk?”

Hello everybody,
I am using NixOs in an air-gapped environment and want to make sure my containers always work.
Currently there is a registry available in the private network, but I don’t want to rely on it, I want to place my “image.tar” on the local system storage and load it from there . I saw the “virtualisation.oci-containers.containers..imageFile” option but it is requesting a “package”, which I don’t really get.
But looking at the source code it looks like it would work if I was able to enter a path to the file.

So yea, I am a bit lost. Is what I want to do is possible?