This is a really neat idea. I'm never sure how close to the airport I should be to refuel- too far out and it might not be "full" enough for return, but too close and you might miss the last gas station!
I got the idea after my girlfriend and I went to Maui for Christmas. I had never been there before, and had no idea where I should get gas on our way back to the airport. Like you said, too close and you might miss the last station. Plus, I was already concerned about missing our flight. The last thing I needed was the extra stress of watching for gas.