General

Personally speaking, I wouldn’t force anyone to do anything they’re not comfortable with. Any relationship should be based on truth above all else, and I have always been quite honest with my partners-although most have guessed long before.
If someone was leaving treats around the house, I’d usually just ignore them unless I knew they were for me.
And if someone called me thin, I’d be pretty annoyed in honesty, I never liked it even when I was, but that could just be me.

This is more "encouraging" and not really brainwashing, which would take away the person's choice completely. (And I think most agree that's not cool.)

So, if you encourage with sex and treats and meals, could you turn someone towards feederism? Not if it's something they're honestly not interested in, however if they're new to it and not against the idea, or if they're on the fence, you could tip the scales in your favour.