I've got an auto as well and manage to get 400km on a tank before I cave in and get some fuel, at this stage it's been sitting just above the 'E' for a while now. This is done on 'grandpa' city driving with full exhaust, FMIC, EBC, pod and piggy back ECU.
I used to only get 250km's from absolutely-full-tank to just above the 'E' mark. I just changed my O2 sensor and then I could reach the magic 400+ mark, then I got my ECU tuned and things seem to have improved a little more still.