Just browsing through Netters and I had a thought. The Cremaster muscle surrounds the Testicles and is responsible for pulling them upward toward the body. All muscle can build strength and even gain a certain degree of size depending on the muscle and individual. Suppose one were to place resistence and attempt to pull with that muscle, the testicles upward. Could the muscle build up enough new fibers to increase the overall fill of your scrotal sac?