Saving money by creative car cooking

My sister Jill recently told me about a new way to save money.  I think it's great and not only saves money but reduces green house gas emissions as well.  

Her husband has a long drive to and from work and so by the time he gets home at night the car's engine is rather hot.  They noticed this one day and made a joke about heating up left-overs on it.  Well, they got around to trying it and it worked.  She just places the left-overs in a pan and when he gets home he knows now to open the hood so she can start dinner.

Since they started using this trick they have seen their energy bill go down as they don't use the oven as much.  As a bonus, she reports he has been getting home from work earlier because he knows she can't start dinner until he does.

Do you have any "crazy" money saving ideas? (how crazy can it be if it saves money?).