I do this all the time.
Just use an air blower (one that has a rubber tip) on your air hose... Fill the corny with your choice of cleaner, connect the corny quick-connect to the corny, blow air into the connector (the pop-off valve will release any dangerous pressure levels), then remove the quick connector while still under pressure.
By the way, there is no fear of contamination even from the worst of air comressors... you're pushing cleaner (and then sanitizer) through the lines, not air.
After the corny has served it's purpose, clean it normally.