See, if he just wants to LOSE it, I don't know. I mean, I know tons of weight exercises that would trim and tone but it sounds like any mention of the word "weight" will get him disagreeing with it.
The muscles in the ass and hips don't tone like the ones in the arms. Not from what I'm seen and experienced. They just get tone and tight whereas the arms, neck and chest get toned and expand.
I think he'd be open to the weight exercises if they were different from what he's tried. He's basically only tried squats. What did you have in mind?