I realize this is a necro, but just in case some future visitor is looking for the same subject matter...
Off the top of my head:
- There's "Addicted to Love Juice" by Cum Bunny, which is archived on Fictionmania.tv.
- More recently, "I Went to Europe and All I Got Was This Succubus Curse" by Schizo, also on Fictionmania.tv
I should point out that while the aforementioned stories contain male characters that are gradually transformed into females through ingesting semen, the catalyst is either via curse or potion.