First of all welcome to the Octopus Forums!
Thanks for reaching out.
Octo pack actually doesn’t utilize the nuspec file at all. If that’s a requirement for your process, I would suggest instead using a script step in your build pipeline or a nuget.exe runner if it exists in your build server of choice and create the package that way. Documentation: Pack - Octopus Deploy
Alternatively, before the pack step, you could manually move these files with a script step to exclude them from the pack step.
I’m sorry I don’t have better news for you.
Please let me know if you have any other questions or concerns.