Unplug all the cables from the computer, including the power cable. Lay the computer face-down, supporting the neck and base with a soft cloth under the screen.
If you do this - don't you still need to apply a fresh coat of thermal paste to the exposed ends of the two heat-sink posts (that separate when you open a G4 flatpanel this far) - my understanding was that the machine would overheat and you'd be left with didley squat!!