You probably already know about it, but there is a place in the chicago area called "hot doug's" that makes duck fat french fries on fridays and saturdays. They also have wonderful sausages.
The Publican, at Fulton Market, makes duck fat fries. It too fills up quickly, but they open at 3.30P every day and don't get crowded 'til 5.30 or so. And: absolutely fantastic beer list. So that's your best bet in Chicago.