Be upfront but professional about it. You don't have to straight out tell them "I peddled porno" but you can simply tell them you marketed "adult entertainment". It's kind of like the difference between politely excusing yourself to use the restroom and loudly announcing "I have to go take a shit!".
Just keep it professional. You want them to think "This guy seems like a real pro" not "this guy seems like a real sleazeball".