[rick3000]

First, I would like to note that just because you have a Porsche and can afford one does not mean you should throw money away and not even care about MPG.
Second, my house is on a hill and recently I started to think along the same lines. I have a manual and all I do is shift into the next gear, that way I can still call on the engine but the speed is not restricted by the gear and I just coast but it is safer than just going to neutral. Not sure about a tip, but auto's are normally programmed for good fuel economy so I wouldn't worry about it.