You absolutely Can! In Spring forest Qigong it is always about good, better or best. As you continue to practice in whatever way feels the most comfortable to you your channels will open and you may find you are able to breathe more comfortably through your nose. It helps to be intentional. Begin your meditations with the intention to open up your breathing system so that you are able to breathe more deeply. When you become a little more comfortable you can try the SFQ breathing for 10, 20 then thirty seconds to a minute and increase from there. But at this point if it makes you anxious just do what feels the most comfortable to you, you will still benefit. Trust your intution. Visualization and confidence are so key to Spring Forest Qigong. You can visualize opening up your sinuses,nose and lungs with white light or whatever color comes to you.
Also practice the active exercise, "breathing of the universe" and small universe, too.