I have seen an herbal supplement called "FlorEssence" work miracles in individuals with impaired or failing kidney function. It actually saved my father's life once. His ureters had completely been blocked off by severe prostatic hypertrophy and he was (unbeknownst to us at the time---though we knew SOMETHING was wrong with him) uremic. I suggested FlorEssence to my mother because I knew it was extremely gentle, but also powerful. I also knew it wouldn't interfere with any medications he was on, as it has no contraindications. It essentially helped him detoxify more efficiently through whatever other eliminative means he had available and he came around in no small way. To this day my mother says emphatically that it saved his life. He was able to get to where he was able to go in for diagnostic work and the state of his kidneys left his doctors amazed he hadn't already died from uremia. He did ultimately end up needing a kidney transplant (since the damage had already been done), but we'll never forget what a profound effect that stuff had on him when it counted.
I also helped a friend who had an older dog with kidney failure so bad they intended to put him to sleep that week. I told her about the FlorEssence and she began dosing her dog. The long and the short of it is that the dog made a miraculous comeback and (continuing to take a little FlorEssence every day) the dog lived another 2 years.
It's mighty good stuff. You might inquire as to whether it is permissible for your father to have any "herbal tea". If so, then this should be safe.
It is most unfortunate your father is being discouraged from natural healing methods. It was diet and lifestyle that got him into this predicament, and it is diet and lifestyle that can nearly always reverse it (if he's ever open to any suggestions, let me know). The adding of insulin to the equation helps in the short term, but will worsen him irreparably in the long term. His doctor is doing the only thing she knows, but she (as many conventionally trained M.D.s---Boondoc excepted) fails to comprehend the physiological principles underlying the condition. It's like they forget everything they were taught about human physiology their first year in med school and just go about administering pharmaceutical protocols like stepford wife automatons...oblivious to their consequences. Out of the 300 most commonly prescribed medications, NOT ONE actually supports or restores normal physiological function. They act as if this condition simply fell out of the sky...or was a direct consequence of some "unfortunate gene" (DON'T get me started). Absurd.
OK--enough of that. This stuff can make me crazy.
I wish your father well. I don't know whether Miracle-Mineral-Supplement would help or hurt him, but this might be a question for the Big Kahuna--Jim Humble, himself. Perhaps you should parlay over to his web site and drop the man a question. It seems to me you'd probably get your answer.