How to display a fullscreen TYPE_SYSTEM_ALERT window?

I'm currently having a hard time displaying a TYPE_SYSTEM_ALERT window in fullscreen mode. I'd like to do so in order to have an overlay view, created from a service, on top of the status bar but without hiding it.

However, putting the FLAG_FULLSCREEN flag in the layout params of the window I'm creating doesn't seem to work. I found the STATUS_BAR and EXPAND_STATUS_BAR permissions but I couldn't find how to make use of them.

Here are the LayoutParams :

    WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.WRAP_CONTENT,
            WindowManager.LayoutParams.TYPE_SYSTEM_ALERT,
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
            WindowManager.LayoutParams.FLAG_FULLSCREEN,
            PixelFormat.TRANSLUCENT);

    params.gravity = Gravity.RIGHT | Gravity.TOP;

    mWindowManager.addView(mOverlayView, params);

Any ideas?

Thank you