How do I initiate a clean windows shutdown without waiting for a user?

Question

I'm trying to make an embedded windows 7 application shut the machine down gracefully.

I've tried this:

ExitWindowsEx(EWX_POWEROFF | EWX_FORCE,
        SHTDN_REASON_MAJOR_OPERATINGSYSTEM |
        SHTDN_REASON_MINOR_UPGRADE |
        SHTDN_REASON_FLAG_PLANNED);

which appears to instantly kill everything (my app doesn't exit cleanly, it just dies).

I've tried swapping EWX_FORCE for EWX_FORCEIFHUNG but that presents the user with a dialog which, in contrast to the docs doesn't seem to offer any timeout.

Is there a way of doing this elegently or do I simply need to record the need to shutdown and then call the forcible shutdown as the last thing my app does?