You've seen this one too?
Thread - NBE Guide
Breast size in relation to endogenus hormone levels... is a pubmed article referenced in it. The abstract tells a lot.
High IGF-1, low androgens (suggesting aromatase), certain combination of high estrogens or high progestogens.
I think a combination of herbs that increase progesterone and estrogens together are useful for a male. Prolactin is highest at night, and massage increases prolactin which is useful too.
Botanical modulation of menopausal symptoms: Mechanisms of action? gives what it believes different different effects of herbs to be:
Progestogenic (Progesterone) - red clover, hops, yam, and chasteberry.
Estrogenic - soy, red clover, kudzu, hops, licorice, rhubarb, yam, and chasteberry
Prolactin (Serotonergic) - Black cohosh, kudzu,
kava, licorice, and dong quai
This paper is very good, but this list is still uncertain. Many progestogenic or estrogenic herbs don't interact strongly enough with the right Receptor Subtype, specifically ER-alpha or PRB, which are both believed to be located in the breast.
Hops increases prolactin, unlike mentioned in the article. Kudzu and Pueraria M are similar enough. Massage can replace Serotonergic herbs. Wild Yam and Fenugreek have the same active chemical, diosgenin, so both are similar in use. Too much Red clover extract may cause infertility. There are safety issues with long term use of Black Cohosh and Donq Quai. Kava is a strong liver toxin.
Saw Palmetto may reduce DHT, but I hear its useful for firming and reducing discomfort and not growth. Since its useful for firming, this implies that it affects the connective tissue in the breast (which contains PRB).