Are you sure its a he and not a she? I suspect its a mature female fish who has over eaten. The mature females have a tendency for that behavior ( if she goes around asking the other fish 'do i look fat?' then you can be certained its a female ). Is the stomach bloated with scales in disarray when you look closely?

The solution is to separate her from the rest and not feed her for about 2 days and make sure she is pooping before you let her join her original tank mates. From experience, the 'greedy' female neons will usually be the ones laying eggs. My theory is that their 'greed' is due to maternal instinct ( i.e they need more nutrients because they want to have babies)
If you have to feed excess food because of the other fishes in the tank and dont want the neon to over-eat then you may have to seperate her for good.
Hope this helped.

ps: If you want to breed neons, I would recommend buying a few neons from different shops ( rather than all from 1 shop) so that they have a bigger DNA pool. If not they are inbreeding from the same stock and the offspring will end up sickly or dumb.