I'm so sorry to here your kitty has CRF. Don't give up hope, he could still have many good years left with you. The vets told me that my cat's severe hepatic lipidosis was fatal (her skin was a strong bright yellow, she was anorexic - a wobbly skeleton, dull eyed and lethargic) and prepared me for her passing many times. But she and I knew she wasn't ready to go (she's a fighter too!) After months of consistent tender loving care, most of it instinctive and holistic, she is perky and pink and sweeter than ever. At 14 yrs old, she's still weak from the fight, but she's not ready to leave anytime soon.
Just let him know that as long as he wants to fight, you'll help him every inch. They do listen, they just don't like us to know they do! =)
Although not completely natural/holistic, here are a few sites that do offer some advice and even support groups.