Hey Robert,
I figured it out. You can write in leaflet.js at the // Google Maps plugin// line 12. You have to slightly change the syntax of the JSON, but it works like a charm. I think it can easily be set to selection options in the admin, even cooler would be a script that corrects the JSON syntax so you can paste whatever the google wizard gives you.
example of the code: var styles=[{elementType:'geometry.fill', stylers:[{saturation:-100}]},] ; map.setOptions({styles: styles});