>Do you know, is it possible from VB Script? It would satisfy his request, I believe.

Nope, no Win32 API calls from WSH, AFAIK. The best suggestion I could offer would be to write an EXE in C++ and deploy that. Something like

#include <winuser.h>
#include <windows.h>
void main(){
    ExitWindowsEx(EWX_SHUTDOWN, 0); // Second param is ignored
}