The following code in the Build.cs of my plugin resulted in the so-file being copied to the package directory :
string LibBinaryPath = Path.GetFullPath(Path.Combine(ModuleDirectory, “…/…/Binaries”));
RuntimeDependencies.Add(new RuntimeDependency(Path.Combine(LibBinaryPath, “Linux”, “libUE4Editor-MYPLUGIN.so”)));
Unfortunaly, the package still refuses to load this file when I starts and throws “please ensure the plugin is properly installed”.