Eatin doesn't really influence how much you can take.
It's stil around 0,25 pr beer you take regardless what you do. Just like you can't run it out of your blood as others think. Also takes a good deal more than one hour to get it out of the system, unlike main belief that it's just one hour. Some even go for 2½ hour for one beer.
Takes pretty exactly 1½ hour for me to get rid of one beer, have alchometer in the car, and common sense
Your friend should have read up on it, but still a bit of shame for him. You're more strict than us, allowing 0,5 in DK. Used to be 0.8, untill some 10-13ish years ago.
You will always get the blame in an accident though, if you have alchohol in the blood,regardless of it being legal, which is a kinda weird way to do it, i think :P