Invite him to play a little game I like to call "Celebrity Fantasy Frankenstein"
"If you could pick one celebrity as your ideal physical form, and a different one as your ideal personality, who would they be? Living or dead?"
EG - "My physical ideal would be Johnny Depp/Chris Evans/Idris Elba, but with the personality of Sir Patrick Stewart/Neil Gaiman/Isaac Asimov."
If he names someone slim as his physical ideal, then that gives you an opening to dig further, e.g.
"Oh wow, yeah she has a great body. So do you think you're mainly attracted to that physical type? Or is it more about the mental connection for you?"
HINT: If he can't readily name someone whose personality he finds attractive, I'd be getting rid as a shallow twat. Even if he says "honestly if I could find a woman like my mum" at least that shows some sort of emotional self awareness.
Hope this helps. I saw your previous thread but didn't post. I'm a size 16 with bingo wings and a big old mum tum. Over the past few years I've gone from being pathetically grateful to anyone who's been remotely interested, to picking and choosing and turning down 90% of chancers.