Get one of his dishes featured in a food column in the newspaper then enlarge it and put it up in the restaurant. Give free meals to local politicians or celebrities then take their picture while they are eating. Food by Mario, so good the mayor loves it. Have the chef greet the diners if possible. If he feels important and you genuinely acknowledge his contributions you've got it made.
Recognition IS very important but nothing beats a fat paycheque.
What I've done for years is given my cooks bonuses based on per-shift sales. This way, when you have a good day, you share in your largesse. When you have a bad day, it doesn't cost you any more. It's also good incentive to maintain the quality and creativity in the kitchen. You might also try profit-sharing based on your NET profit.