Actually, start jerking off as many times a day as you can for about a week or so(not sure how much time you have?). You'll notice this increases your production. Then do nothing(sex or spanking) for a day or two, then shoot her full of goo.
And going off of something I got from (I think it was)Cy Wilson, if you give your girl M it will make her ovulate, which is what is needed for conception.
Last note: You may already know this, but research shows that if a woman comes the chances of conception are increased exponentially. They have video(don't ask me how they got it in there) of a woman coming, and it shows her cervix dipping down into the vagina rythmically with the contractions. The point being, if you play it right, it's dipping down into your school of swimmers, making the trip that much easier for them.