After doing some research we decided to try two methods of inoculating corn smut into a few of our maize plants. The first method, as I read the Aztec's did to their maize plants so they could harvest huitlacoche, is to score the base of the stalk. Since the fungus is water-borne this helps the spores travel upwards to the ears. The other method is "silk-channel inoculation"; simply apply some of the fungus spores to the silks of the ears you wish to infect. There is a lot of recent research on this method, regarding timing and growth stages, as huitlacoche is becoming a sought after ingredient in a lot of kitchens and can be a more lucrative crop that corn. Unfortunately, all the research I came upon was too "science-y" (i.e. long and boring and full of unpronounceable words) for me so I just went ahead and did it; I wouldn't have been able to make the corn any younger anyway! 
First we harvested the big ears from the stalks (and threw them right into a pot of boiling water for lunch!) we wanted to inoculate. Then I scored the stalks at their bases, about 4 or 5 cuts per plant. Then with a small piece of the fungus that is already growing I applied some spores to the silks of the ears where we want huitlacoche to grow and around the base of the plant. Then a good watering. Now we just sit back with our fingers crossed and our mouths watering!