There was a game, I forgot what it's called (maybe
Choo-choo remembers?). Yes, it's a (low-)fantasy, and dickgirls are not the game's main focus, but you do get it as a viable option. Basically, it's a Ren'Py game with renders made in 3D Sex Villa.
The protagonist is a geek in either high school or college, he comes across a bong that turns out to be housing a genie. You're then given a choice of what to wish for. One of the wish choices is to get revenge on a mean popular girl, which results in her growing a dick, and if you do everything right (or wrong, depending on how you look at it) in the following choices, the PC will end up in a romantic relationship with her as a dickgirl, and he will be the top. I say that this is a viable option because she is romancable in most choices.
Sadly, the game is pretty short.