Do the front pipe - get a Nistune and a good tuner and tell him that economy is a priority. You shouldn't need two boost settings you have a controller called your right foot!!
You should be able to get it down to 12L per 100km. Then there are the usual things - don't increase weight by carrying unnecessary junk around in your car, keep tyre pressures up - anticipate the traffic ahead and don't brake unnecessarily etc. Tune it on 95 but not less.