Local NuGet feeds during build

I’m trying to get my app working in a docker container. I’ve set up a build process, but it needs to restore nuget packages from a local feed (https://docs.microsoft.com/en-us/nuget/hosting-packages/local-feeds). This local feed is kept on a file server, \file-server\NuGet. This all works fine and dandy when running on my version.

I can’t mount a drive during a build operation. I’ve tried using ADD/COPY to pull a version of the files, but because they’re not in the original package, docker doesn’t work. I’d like to avoid setting up a local NuGet server if possible.

How can I let docker access the file server during build? For context, the docker image is windows.