I just thought of something . What if there was a breeding station? We have other type of experiments that help train up your other skills beyond the procedural sex so why not something for the breeder and fertility perk trees?
Your character could be paid for the amount of seed you donate or the number of children you give birth to. It could happen over the course of maybe 4-5 days or just restrict it to an overnight thing. You could even have a small side quest where the stuff the doctors inject into you in order to increase 'production' causes to be stuck in a permanent rut/heat. (I know that ruts aren't implemented but I just thought it'd be interesting)
You don't have to do it if it's too much work. It's just a suggestion.