Buy a tank of Argon, attach a hose to it, put other end of hose in the bottom of a bucket, fill bucket with argon gas. Argon is heavier than air and will push the air out of the bucket, like you were adding water to the bucket. Argon is colorless but you'll be able to feel a temperature difference between the argon and the air. The argon will be colder than the air because of its rapid expansion as it leaves the tank.
Now, put your previously sanitized cumjar into the bucket and fill it with argon as well. Cum in the jar, seal the jar, and remove from bucket. Place the jar in your freezer or fridge to extend freshness.
Be aware, argon is an asphyxiate, so make sure you work in a well ventilated area if possible.
