Congrats on such happy lilies, but I agree shorter would be better. You are correct in that a fertilizer high in nitrogen encourages taller lilies and lawn foods with the first number highest on the fertilizer ratio listed on the bag often cause this taller flower growth. A complete fertilizer like Osmocote Plus made for flowers and vegetables is a better choice for bedding plants and perennials. It is a more "balanced" plant food with the three number or the "NPK" ratio less weighted towards nitrogen the first number.  This year there is not much you can do to shorten the lilies so stake them if needed and enjoy the drama of the tall blooms. Wait until after the lilies bloom to apply the Osmocote as the growth later this summer will produce blooms for next year. By not feeding while the lilies are in bud the blooms will last longer. Keep growing, Marianne Binetti