如何以编程方式在外部SD卡上安装应用程序？

I´m currently developing an app which works as an Update Manager. So far the app has work great whenever I installed or updated any other app. All these apps have been installed on the data/app folder and I have used the android.content.pm.IPackageManager class with the installpackage() method to install them.I´m currently developing an app which works as