There isn’t any natural way to stop him to my knowledge, no. You can’t confront him about it, you can’t send him to jail for it. I suppose you could kill him off somehow, but I don’t know if you want to get rid of him completely. :p If you did want to, I guess you could also just delete him.
I know you didn’t want to hear cheat suggestions, but just in case you decide to use that last resort, your best way to go about it would probably be to use cas.fulleditmode, take him into CAS, and just remove the trait and replace it with another. It’s pretty harmless- but I get not wanting to cheat your way out of things.
All-in-all, this is why I never use the kleptomaniac trait. I thought I was going to love it when it was first released, but it drastically annoys me. Especially while having tons of Sims.
