I suspect that the reason this one writer gets so many boosts is that the recommenders realized that their likelihood of getting their $45 per successful recommendation is much higher if they recommend his articles than those of most others.

Instead of limiting how many boosts one writer can get, limit how many $45 bonuses a recommender can get per month per writer. Then, a great writer can still get many boosts, but only if many recommenders give him or her recommendations.