Second, POI (Point of interest) files have nothing to do with what I think you are talking about here. What you want to do seems to be to get instant fuel economy reading from your car so that you can drive in such ways to improve you EPA. You can do this with an OBD-II scantool from the mp3car store and usually any OBD-II application installed on either your phone or a dedicated car computer of some sort.
I wrote a simple app for meego that does this:
Basically you drive in such a way as to make the circle as big and as green as possible. When you drop below your target economy however, the circle turns red indicating you better change your driving habits. You can set your "goal" economy with the slider.