To feed a Kentia palm like this, apply some three-month slow release granules and scatter them on top of the soil and work them in with a fork, and then lightly water the soil mixture. Personally, I like Osmocote, but that's probably because it's what I see when I'm shopping at Walmart. Get any kind you like, preferably on sale, as long as it's slow release. If you prefer a water-based plant food, dilute it to 1/2 the recommended amount, and then apply as directed.
Of course, you don't want any of this to show, so move the moss out of the way, and replace it neatly when you're done. No one will ever suspect! And you can keep the secret if you like.