It was published in the early 90’s in Aboriginal SF.
The title of the story was “The Secret Identity Super-Diet” or something to that effect. It was about a mild-mannered (and very overweight) patent office clerk who ends up foiling a Brazilian plan to use horse pistols with superconducting round shot balls to take down the stock exchange and gain a huge economic advantage.
I would love to know who wrote it, and best of all to find out which issue of Abo it was in so I can replace that hole in my library. (Some draconian house cleaning by a well-meaning housemate took care of 95% of my old Abo’s.) Or at least if it’s been collected in any mass market book.