Allowing Fullscreen Applications To Overlap Taskbar Under Windows 7?

I need to allow full screen Windows applications overlapping task bar under Windows 7. The "auto hide" is not the option due to user requirements. One possible solution is to change the code of those applications to allow them overlapping task bar, but it will imply a lot of work as we have many of them already running at customer's side. The best would be just to remove programmatically the "topmost" style of task bar window, but my code failed to do that with the error 0x00000005 "Access denied".