To me, the various "step on a crack, break your mama's back" sabbath rules are less of a point of conjecture than the cheats some "believers" have developed to work around said rules. Cafeteria Catholics are one thing, but it is truly perplexing that someone would take the time to modify existing pieces of standard equipment like telephones and elevators just to avoid pushing buttons.
One would think that the spirit of the Melacha rules, aside from showing compliance with the rules, is to encourage the believer to use the sabbath day for contemplation and reflection. Or not; maybe the rules are just there to make sure people obey them. In either case, what is the urge there to try to find ways to sneak around the rule?
Apparently this hot plate work-around -- and the house fires that start when they're left on for too long -- is commonplace in these communities, which makes you wonder if they can't just make a sandwich or something for the night, have some cereal, something that doesn't require you to leave a dangerous device plugged in all night. No deity worth worshipping would seriously expect you to endanger your life and your family's lives with obsessive rule-following.
Perhaps instead of finding inventive ways to squint around the foma, it might be more productive -- and intellectually honest -- to simply decide to obey them, or not.