If you have UAC off, it doesn't take much of a script.
If you have the Update Channels enabled, it will update itself whenever there is a pending update at next launch. So, you just need to quit and re-launch MC with the Auto-Updater turned on, basically. Run through the MC installer manually once, and make sure to check the "next time auto-install after 30 seconds" box, so that it can automatically run through the installer.
Then, you just need to script a shutdown of MC (including the Library Server), and then a startup again a little bit later.
To force MC to quit (including any Library Server running in the tray) use:
mc20.exe /mcc 20007,1
To start MC back up in full UI mode use:
mc20.exe /start
To start MC back into Library Server Mode use:
mc20.exe /MediaServer
You should put a good long sleep in-between the two (maybe 30 seconds or so), as MC takes a little while to fully shut down.
Also, I strongly recommend against running with UAC off.
I definitely agree here. UAC is a valuable security feature if this is a machine that EVER gets used from the console (with a keyboard and mouse). If it is really a headless server running in a closet that NO USER EVER TOUCHES DIRECTLY, then perhaps this is a good plan.