private void TranslateRootVisualY(int yNew)
{      
  var rootFrame = Application.Current.RootVisual as PhoneApplicationFrame;
  rootFrame.RenderTransform = new CompositeTransform() {TranslateY = yNew};
}
In your case, you can eliminate the automatic translation and make ScrollViewer scroll to desired offset in GotFocus event:

private void firstNameTxt_GotFocus_1(object sender, RoutedEventArgs e)
{
   TranslateRootVisualY(0);
   Dispatcher.BeginInvoke(() =>{
      double destOffset;
      //...calculate destination offset
      ContentPanel.ScrollToVerticalOffset(destOffset);
   });
}