I can. It's easier to do it with your index and middle finger of both hands. Start practicing this way. Use those two fingers on both hands to push underneith the tip of your tongue, so that it folds back. The bottom of your tongue should almost be touching your lower lip, which should be pressed down and back by your fingers. There should be a gap between your upper lip and your fingers. Use your lungs and blow. When you master this, switch to the index finger and thumb from one hand, forming a partial circle.