I know this is far from an outrageous FE idea, but perhaps it's one that is so simply it's overlooked?
Don't fill you gas tank over 1/2 a tank, or even lower than that if you have a large tank. You'll save the extra weight of all the gasoline.
Has this been suggested? It's just something that popped into my head earlier today. I can't do it unfortunately because I have to fill up to get readings, but some with a scan gauge would do well to use it.
Here's a thread on it. It did not make a noticable difference for me running 5 gallons opposed to 15.