sirrogate
A "substitute papa" --- i.e., a sperm-donor for a couple who are unable to conceive on their own due to da man's being being unable to effectively inseminate da woman.
Telling a hot chick dat you want to be her sirrogate may indeed be a way to get her to let you slake your lustful cravings for her, but if she does indeed get preggo afterwards, said professed wish might not hold up too well in child-support court, especially if (1) she had not actually "had anyone else" at da time of said delightful "encounters" wif her, and so you hadn't even truly been "replacing" or "supplementing" some less-than-virile male whom she'd also been being intimate wif, or (2) her "main squeeze" partner hadn't even known/approved of said "getting some on da side" actions dat you and she partook of, and so most likely it wasn't even as if he'd ever actually expressed a wish to have his sweetie-pie obtain a tummy-bump off of some other dude!