I believe the story you are thinking of is "Frank" by Robert Reed, which was indeed published in Interzone, issue number 154 (April 2000), and which can be read online at the Internet Archive (link).
Blurb:
The multiverse is infinite, and that infinity is populated with an
infinite number of Franks. A very specific Frank. And it so happens
that one of these Franks is very successful, and also very willing to
shout across the multiverse to the lesser Franks, telling them what
they should do to improve their sorry existences.
This arrogant man needs to be humbled.
"A standard commercial plays in the background. Orchestrated music
swells into the booming voice of an announcer. 'The most successful
man in the known universe has finally published his riveting life
story. Learn the true story of Gossamer, Incorporated. Experience the
dizzying ride of his life. And enjoy the perspective that only the
great man himself can offer. FRANK JOHNSON, THE VIEW FROM THE CENTER.
Now on sale at quality bookstores on a million enlightened earths!'