I would use the air force as they had to initially destroy the red air force on the ground. Then smash my way across the Ukraine, Romania and the other coutries under Russian control. And treat them as liberated countries thus ensuring the enlistment of people to fight against the Russian army. And finally i would have secretly talked to the Japanese about starting a front in the siberian area. Although this would have been a fearful trouncing for the Japanese it would have kept valuable resources from fighting the Germans, thus giving them a rapid advance across the country.