I normally end up using a LORA (this one is pretty good).

I have had some success using the URPM for blowjobs, but it's still pretty luck-based. Ultimately, adding additional anatomy (a dick or another intertwined person) seems to be pretty difficult to get right. That's why there's so many posts of just a single naked woman in portrait with the hands out of frame - it's just really easy to make those prompts work.