Gentlewoman:...or have a partner who is, etc. Weight gain just not being in the cards: how do you enjoy this fetish? What do you do to fire up your imagination? What does your foreplay entail?
I'm eagerly anticipating any and all replies!

This is always of interest to me, especially now that I am in a job which is physically demanding and I really can't get fat or I'll lose my job.
When I had a desk job, it really didn't matter and I could just balloon up into a big old butterball.
One thing to add: Have a physically demanding job, or make it as physically demanding as you can. Walk to another office instead of emailing. Take the steps. Park a half-mile from your work (or farther).
Let's not forget that the brain may be the most powerful sex organ any of us have.
Imagination, roleplaying, reading erotica, "naughty" talk, all these can help contribute to the enjoyment of this fetish -- without a single calorie being eaten or a single fat cell being formed.
Also, it may not be that important how much is fed but the manner in which it is fed, depending upon the relationship.
Best to you in your pursuits of pleasure (without plumpness).
Zonker