Always a delicate matter. Be careful with the gum / freshening sweet option or you may end up with: "Smells like someone took a dump behind a pine tree".
I had the same kind of problem years ago. Very strong body odor, same clothes day in day out for more than a month. We tried being nice, nothing happened. Even the boss talked to him, nada. He finally resigned with a lot of theatrics about not being appreciated, etc... I believe that he didn't take too well the 3 bars of toilet soap someone left on his desk along with a scrubbing brush.
That someone being yours truly
