var installer = WScript.CreateObject("WindowsInstaller.Installer");
var database = installer.OpenDatabase("TestApp-1.0.msi", 1);
var sql
var view

sql = "SELECT File from File where FileName='TestApp.exe'";
view = database.OpenView(sql);
view.Execute();
var file = view.Fetch().StringData(1)
WScript.StdErr.WriteLine(file);
view.Close();

try
{
    sql = "INSERT INTO `CustomAction` (`Action`,`Type`,`Source`) VALUES ('ExecuteAfterFinalize','2258','"+file+"')"
    WScript.StdErr.WriteLine(sql);
    view = database.OpenView(sql);
    view.Execute();
    view.Close();

    sql = "INSERT INTO `InstallExecuteSequence` (`Action`,`Condition`,`Sequence`) VALUES ('ExecuteAfterFinalize','NOT Installed','6700')"
    WScript.StdErr.WriteLine(sql);
    view = database.OpenView(sql);
    view.Execute();
    view.Close();
    WScript.StdErr.WriteLine("Committing changes");
    database.Commit();
}
catch(e)
{
    WScript.StdErr.WriteLine(e);
    WScript.Quit(1);
}