Please someone correct me if I am wrong about progesterone induced gyno but according to medical literature, except in those cases where strong synthetic progestins, like medroxyprogesterone, were administered. In these cases the gyno is due to suppression of LH and testosterone by the progestin, NOT by a direct effect on breast tissue. On a cycle your LH is already suppressed by the AAS anyway.
Breasts have two components: alveoli and ducts. The alveoli are what secrete milk; they drain into ducts. Gynecomastia is the result of ductal hyperplasia, not alveolar hyperplasia. Estrogen stimulates the ductal tissue, while progesterone stimulates the alveoli. Alveolar hyperplasia does not contribute to gyno. If you want to read more on breast development, I suggest visiting this site:
http://www.endotext.org/male/male14/male14.htm
Two drugs that have shown the greatest efficacy in treating gyno are nolvadex and Raloxifene another SERM. Nolvadex has been around longer but newer studies show that Raloxifene is supperior in attacking the problem at its source, the estrogen receptor. Bigbadasian is right, the consequence of running nolva throughout the cycle is a lowering of your IGF-1, not a good thing for making gains, but to me and people who are gyno prone an important option for prevention.