I am so sorry to hear that
Here are a list of excellent quality foods that are low in phosphorus for your kitty:
From this thread: http://www.pets.ca/forum/showthread....ghlight=bengal
. They are probably a much better quality and not as expensive as your vet food.
To stay within your grain/by products free wish other foods with good low phos numbers: EVO 95% Chicken & Turkey, Felidae Grain Free Salmon, Felidae Grain Free Cat & Kitten, Wellness Kitten, Wellness Beef & Chicken, Wellness Core Chicken, Turkey & Chicken Liver.
Of course canned is best for him as it makes it easier for him to get his fluids as opposed to dry. No kibble should be fed, unless it is to transition him to a new diet.