Perhaps you and your wife could find a way of letting you indulge in your fantasy without actually involving another person.

How about roleplay and a blindfold and of course with your wife's willing consent. If you are blindfolded she could roleplay that she is as many different people as you desire and with the addition of sex toys such as the type that is an imitation of a woman's intimate sex organs you could have your three some without the need for a 3rd person