I can sympathise completely - I have a similar situation right now - my resident 18 month old boy is huge, but lanky, and he isn't much of a "foodie": he eats two small pouches of wet food a day, with occaisionally a handful of dry food in a treat ball. Skye, our new girl, is only 5 months but eats like a horse - ok, she's growing, but she eats more than Riley did at her age, and she'll grab anything going.
I've taken to feeding Riley on top of his cat tree in the front room, while Skye is fed at the same time, but on the floor in the kitchen. When Riley has finished "picking" at his food, I cover it with a small side-plate, and remove it whenever he goes to nibble some more. It's a hassle, but as they get fed while I am in (brekfast-time before work, and dinner after I am home with treat ball available during the day), it's not too bad. It seems to work - by seperating their feeding areas, they are going to different locations to eat when hungry, and if Skye goes for Riley's food, she can'y get to it, so will hopefully learn that it's not even worth checking.
Good luck with it - I know it can be a real pain, but it should help, and hopefully your new fluffy will learn with time to calm down on the guzzling, since food is regular, consistent and predictable. It can be difficlut to keep their weight under control if you have a "foodie" (like Skye - some cats, like people, seem to enjoy eating even if they aren't hungry). Our ones are indoor cats, so we have to be pretty strict - it's not like they are out all day climbing trees or hunting to run it off!