Still no luck. Based on looking at the save files fulfilling desires during sex seems to boost loyalty way more than lewdness, and I'm not finding any action that raises lewdness faster. I'm not using advanced rules at the moment since I'm trying to do it with a starting slave, and anal weather doing it to her or using aphrodisiacs to get her to agree to sex on day 1 and making her do it herself it still doesn't beat loyalty gains. I'm starting to think if you have your starting slave start with pliable you're just going to get devoted no matter what. There doesn't seem to be a way to force lewdness up faster than loyalty.
As a side note, the desires to have pussy used seems to be broken. No penetration position seems to fulfill it.