I have practised for several years a hold back of the semen. I learned it in a Tao book I read. Basically you press a finger in the hui yin area (se the diagram at the link) when you masturbate. When you ejaculate no semen goes out and it resirculate in your body! You can also train the muscle to hold back instead of using a finger, but that is for the experts.
"It usually takes ten to twenty seconds for the ejaculation urge to pass and to pump the energy upwards, this will result in a partial softening of your erection. It is very helpful at this point to have a lover who is cooperating with you on this and will stop moving and draw her sexual energy up as well. However, it is in fact almost impossible to learn this technique during actual intercourse. Thus solo practice is recommended at first, as you probably will need to really concentrate on the matter in hand! After a couple of weeks of solo practice, perhaps ejaculating once every other time at first and then building up in your capacity for holding in, it is time to start using semen retention in your lovemaking. By then you should have enough self control at the point of ejaculation to hold it back.
Semen retention is a safe process that has been practised in the East for thousands of years. The testicles are constantly reabsorbing any sperm that is not ejaculated, and the prostate gland is likewise reabsorbing unused semen. This is a natural bodily function without which we would get sick, as old semen would ferment after every arousal without a resultant ejaculation. When you actually make love without ejaculation you produce even more semen and sperm and so there is more to reabsorb, so you have to build up your capacity to do this gradually otherwise you will get achy balls. The younger you are the more you will need to ejaculate, so perhaps once every three days is a good goal for a man in his twenties while once or twice a month is suited to a man in his forties. The rate at which you ejaculate though can only be really judged by yourself, but as you experience the benefits so the old compulsion to regularly ejaculate will diminish. It is a good idea however, to not get obsessive about retaining your semen. It takes a fairly long time to become really adept at reabsorbing the energy and semen and so as the pressure builds you will need to release it."
http://www.union.source.co.uk/rebirthofthelove.html
With this method you can mastrubate more often, and not to worry about loosing sexual energy!
