sorry to double post, but in response to your original question about aeromods for the car, I would:
-delete the passenger side mirror if everyone who drives the car is comfortable with that
-Grill Block as has already been suggested
-Zip tie on some smooth wheel covers. This would be the biggest aeromod that is easily removable
-inflate tires
-The car already sits pretty low, so I'm not sure an air dam would work out. Maybe you can take a picture of the underside of the car for us so we can see how aerodynamically "dirty" it is
Check out this thread for ideas too:
http://ecomodder.com/forum/showthrea...dan-21406.html
he modded a 2011 Ford Fiesta which is similar to your c-max.