I'm surprised the vets you've spoken to are not attempting more aggressive treatments in order to bring those numbers down & help Peedee feel better.
I would suggest making sure that Peedee finishes all his meals, even if you have to dress it up with treats, if he's acting hungry and wants more feed him a bit more. It is so very important for kidney cats to eat consistantly especially since he's already lost weight.
You may wish to ask about Phosphorus Binders in particular you would want an odourless & tasteless Aluminium Hydroxide Phosphorus Binder
which can be purchased from the pharmacy - do not
get the one that is peppermint flavoured. You also want to make sure that you do not
get one that contains Calcium, as Peedee's blood calcium is already too high.
Phos binders will attach to the phos in the food in order to prevent absorbtion of even more phos. This should be given two hours apart from the famotidine as the phos binder may counteract the absorbtion of famotidine.
You may also wish to ask your vet about Azodyl
a kidney specific probiotic that helps reduce the BUN & Cre