Bilby's right, it does work. Ripening fruit gives off ethelene gas. The gas itself will speed the ripening process along in other fruit. You might want to place the fruit (in paper, not plastic!), on top of a refrigerator to help speed the process along.
Green mangos are used as vegetables, so a green mango salsa might be right up your alley, like Bilby said.
Peace, Love, and Vegetable Rights!
Eat Meat and Save the Plants!