Spray the surface area of your cleats evenly with a leather protector spray. This will prevent the leather from warping when you do submerge them in water. Allow the leather protector to dry and fully penetrate for at least two hours.
Fill a basin with warm water. Submerge your cleats in the water, until they are fully saturated. This will cause the leather to shrink and pucker slightly.
Set your cleats on a towel in direct sunlight until they dry. The sun will not only dry them, but will facilitate the shrinking process even more. To speed the process, you can shake the excess water off your cleats and then put them in the dryer.
Put the shoes on once they've dried completely. Your foot and toes will push against the leather, forcing it to mold to your foot. Since the leather remains stretchable, no danger of shrinking the shoes too much exists.