"L/100km is sillyness"
Is it?
Why would you want "MPG" in a country where gas is sold by the liters and distances labelled by the KM? If you just want the reading to swing the other way because you're used to numbers going UP on the highway and DOWN while idling instead of l/100km going UP while idling and DOWN while on the highway, I suggest to just get used to it. If you disagree with l/100km because you want a [distance driven/unit of fuel] ratio and would like km/L, I also suggest that of the 3 accepted fuel economy displays, mpg, km/L and L/100km, I suggest that L/100km is the only reading that actually, intuitively lines up to actual fuel usage rate: Use more fuel, number go up, use less fuel, number go down.
How are you not happy with mileage while averaging 9ish L/100km in winter? I drive a short distance to work of nothing but hilly city on studded tires and winter has me averaging around 12l/100km. On a beautiful summer drive the car is an economy beast and runs in the sixes, just 1/100km more than my motorcycle used to.