I did that kind of milage in a mini a few years back when I was promoted. Well actually more as it was 100miles a day I was covering! Used to use 2 tanks in the mini in a week! So I bought a diesel, cost the same in fuel and the economy was only a little better but I was able to do the weeks commute on 1 tank! lol Made logical sence at the time.
The 1.6 isn't known for being the most economic car in the Stilo range, but if its motorway milage (you've not said) then getting 40mpg should be do-able if you do 65mph say with gentle throttle.
If its back road driving stick to 55mph tops, and again try to be gentle with your right foot! Don't worry about folk passing you, get a good calming CD or tune into Classic FM (it really works in slowing you down), deep breaths and just enjoy the drive and you'll be amazed at your sudden increase in economy.
Alternately, drive like Twincamms did in his 1.6, get 20mpg and destroy your tyres, have a great time on the back roads cutting everyone up and driving like a hoon.... welcome the heart attack when it comes! lol