// Set the path to the zip file and the name of the document library
string path = "c:\temp\testfile.zip";
string documentLibraryName = "WSPListener document library";

// Get the central administration web application and the upload folder
SPWeb centralAdminWeb = SPAdministrationWebApplication.Local.Sites[0].OpenWeb();
SPFolder uploadFolder = centralAdminWeb.Folders[documentLibraryName];
bool replaceExistingFiles = true;

SPFolder myLibrary = centralAdminWeb.Folders[documentLibraryName];

// Open a file stream to add the file in the document library
using (FileStream fileStream = File.OpenRead(path))
{
   SPFile spFile = myLibrary.Files.Add(fi.Name, fileStream, replaceExistingFiles);
   myLibrary.Update(); // save the file

   // Get the corresponding SPItem to update some properties and start the installation
   SPListItem item = spFile.Item;
   item["InstallationStartTime"] = null;
   item["InstallationEndTime"] = null;
   item["InstallationStatus"] = "Install";
   item["InstallationResult"] = "";
   item.Update();
}