How to include a file into the game build?

My native plugin needs a large-ish binary data file, which it reads via C fopen/fread functions. Note the “large-ish” part, so storing it as a resource and then copying to the filesystem at runtime is undesirable.

Is there a way to have Unity include it into the build as a loose file?

using UnityEngine;
using UnityEditor;
using UnityEditor.Callbacks;

using System;
using System.IO;
using System.Collections.Generic;
public static class PostBuild
	static void OnPostprocessBuild(BuildTarget target, string pathToBuiltProject)
		string path = Path.GetDirectoryName(pathToBuiltProject) + "/" + Path.GetFileNameWithoutExtension(pathToBuiltProject)+"_Data";
		FileUtil.CopyFileOrDirectory ("Assets/somefolder", path+"/somefolder");