Duplicate setup.exe into an identical executable and point Active Setup to that executable instead.

chrome/installer/setup/install_worker.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This file contains the declarations of the installer functions that build
 // the WorkItemList used to install the application.
 
 #ifndef CHROME_INSTALLER_SETUP_INSTALL_WORKER_H_
 #define CHROME_INSTALLER_SETUP_INSTALL_WORKER_H_
 
@@ skipping 137 matching lines @@
                                  const Product& product,
                                  WorkItemList* list);
 
 // Adds Active Setup registration for sytem-level setup to be called by Windows
 // on user-login post-install/update.
 // This method should be called for installation only.
 // |product|: The product being installed. This method is a no-op if this is
 // anything other than system-level Chrome/Chromium.
 void AddActiveSetupWorkItems(const InstallerState& installer_state,
                              const FilePath& setup_path,
+                             const FilePath& temp_path,
                              const Version& new_version,
                              const Product& product,
                              WorkItemList* list);
 
 // Unregisters the "opv" version of ChromeLauncher from IE's low rights
 // elevation policy.
 void AddDeleteOldIELowRightsPolicyWorkItems(
     const InstallerState& installer_state,
     WorkItemList* install_list);
 
@@ skipping 43 matching lines @@
 // currently being installed -- can be empty on uninstall.
 void AddOsUpgradeWorkItems(const InstallerState& installer_state,
                            const FilePath& setup_path,
                            const Version& new_version,
                            const Product& product,
                            WorkItemList* install_list);
 
 }  // namespace installer
 
 #endif  // CHROME_INSTALLER_SETUP_INSTALL_WORKER_H_