Step 1) Fart a lot in her presence during oral sex and regular fucking. Do this for at least 3 months or until she gets used to the smell of your rancid bowels.
Step 2) Let yourself splatter a little bit when you fart during intercourse... like on her pillow case and shit. This way she'll rub her face and sleep on a small part of your feces each and every night.
Step 3) GO FOR IT! Shit yourself during oral sex and/or while banging the snot out of the bitch. Act completely embarassed when this happens, "I agree that was awful! I never want that to happen again!! Let's take it into the bathroom next time, because obviously you turn me on so much I just have to shit myself silly whenever I cum!"
Step 4) Enjoy your Blumpkin filled life together.