The first, "the pattern of electrical potential flowing through the laptop's metal parts..."
What about multitasking, that would change the feedback, though I am confused why there would be electrical potential through a heatsink, that's why I am saying feedback.
Also the last method, audio, vibrations. Multitasking? Dynamic overclocking, couldn't that easily modify the 'system noise' so much that there is no way to know what is going through the CPU registers?
Perhaps 'rotating the clock frequencies' and voltages randomly within some narrow window while running another thread that takes a few percentages of each core and bounces around the core would fool this?
Ha