Having just done what I could of the Cinderella Classic in 30mph headwinds, I'd say you can use wind as a hill model any day it's blowing, which is most days in Chicago. Do headwind repeats, headwind intervalls, headwind endurance ... It'll train your hill muscles and your hill psyche. And when you're done for the day you can turn around and have a tailwind home ... unless the wind turns too. Check the Cindy ride reports down there in the California section, you'll see what I mean.