Be sure to tell him how attracted to him you are. And don't be ambiguous about it.

A friend of mine once said that the thought most guys, on some level (some deeper than others) are gainers. So just tell him you think his chub is sexy and you'd like to see if he can gain a little more weight.

This made me laugh, you know they do say that parsimony is often the answer.

Part of how you digest food is through emulsification, and belly-rubs would aid this process. It would also help squeeze air out of the stomach, and thus create more room.

I also have a feeling that, even aside from those, it would be helpful by giving you another sensation to focus on. Rather than any pain in your stomach. And that might help you eat a little more.

^^^That's my thoughts exactly. If it's ridiculously fattening then I get much more out of it than if it's something mid-level fattening like, say, a pizza buffet.

Heavy Cream and Chocolate milk are a very stimulating one. And Little Debbie's cakes are another one that get me going.

Public stuffing does it for me too. I like to think that people are looking at the "Big Fat Guy" in disbelief as he puts down his 30th slice of pizza.

I hope you find what you're after.

You could also print a copy of this out. It might be helpful in diffusing his disappointment.
danceswithfat.wordpress.com/2013/04/01/what-to-say-at-the-doctors-office/

There's definitely an audience for "Fat" fanfiction. Feel free to post. It sounds pretty interesting.

I would love to have a feeder who'd want me to put on a large amount of weight. (Read that as a goal of more than 800lbs).

But as Krydrita says, it'd be tricky unless you were just independently wealthy.