The default taskbar on windows 8 is quite nice, and honestly yours will never be a perfect clone.., It would be great if you could allow users to overlay your system tray, on their secondary windows 8 taskbars..

I know rainmeter can stay above the taskbar in most instances (if you set a skin to 'stay topmost')
it does go below the taskbar briefly when the start button is pressed, or the taskbar itself is clicked diretly (not items pinned/running from the taskbar just the taskbar itself)

so its atleast possible, and there might even be a better way, that will reduce or even eliminate this 'blink' when the above 2 events happen