Change units for fuel cost?

So every time you fill up, the Prius pops up a message suggesting that you enter the new ECO Fuel prices so that it can calculate your fuel costs (and savings if you've set up the comparison car's MPG).

However, it asks for the price in £s per Gallon, which is wrong for the UK, given all prices are quoted in £s per litre (even though, oddly, all fuel economy values are still quoted in MPG).

Sure, I can just multiply by 4.55 every single time I fill up, but you'd think there'd be a simple setting to switch between Litres and Gallons?