I just thought of a great suggestion to give you. You know how the town obesity rate descriptors sometime mentions mobility scooters?
It'd be awesome (hot) if you added a way for the girls and the player to get one. My idea is that a mobility scooter, when bought, would allow the player or the girls to leave the house when they're at the immobile weight stage.
You could even allow it to be bought ahead of time from high street shops and let the player toggle when they're using it and when they aren't, creating some tantalizing dialogue where the player buys it even though they're skinny and slowly fill it out as they gain weight.
And it would take a persuasion check to convince a girl to get one. One that gets increasingly easy to pass as they gain more weight. And of course, a feedee girl will be far more willing to get one even when skinny, being turned on by the idea of never walking as a way to burn less calories.
Just an idea I had when my hand was in my pants.