I hear that the shutdown option you desire was requested during the beta of Windows 7 but the request apparently went unheard.
Sorry but, about the only thing I can suggest is to change Windows Updates' settings to allow you when to decide to download and install the updates when you have the appropriate amount of time to do so. My Win 7 system is set to that option so I can't say what the Download updates but let me choose whether to install them option will give you another shutdown option that does not install updates.
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