You have to choose "Use your tits" when she asks what kind of sex you want.
As for the fan fic, that was a commissioned work. Most of the content in the fan fic will never be in the mod. Part of the point of it was to explore stuff that can't or won't ever be in the mod. It's basically an alternate reality where Anon was really hung before something happened to give him a micropenis.
Even if I wanted to make the mod like the fan fic, you understand that drawing and coding are a lot harder than writing, right? Getting the mod to do what it does was a lot of work!