heres an idea.
make a new text file on the desktop, and change the extension from .txt to .bat
right click -> edit.
write the following in the box
now, look through the start menu and find the start up folder, and right click -> open it.
now, paste the .bat file into the startup folder.
Windows key+R and type MSCONFIG.
see if the .bat file appears in the start up programs list.
this file will instantly log him out as soon as he logs in, and only a quick flash of the CMD will be visable before the login screen reappears.
there are no 'simple' ways to resole this, however.
EDIT: actually, i lie. This can be resolved by holding down SHIFT from the point of log in until the OS is loaded, but he wont think of that.