For reference:
run window update from command line? - Windows 7 Help Forums
"yes, you can run it from the command line
%windir%\system32\wuapp.exe startmenu
works but it brings up the gui"
(I find it only works when I remove "startmenu")
This works when adding Windows Update as a Custom item/custom link in Classic Start Menu (Classic Shell) to check for updates, and presumably also in Run.