Renal failure.

Care and diet for young dog in last stages of renal failure...
My sister's dog, Marley, was diagnosed with renal failure at end-November 2010 (the vet thinks it is most likely genetic because of his age). He was very sick at the time of diagnosis and was given IV fluids and then put on a diet of Hills K/D. The vet was pleased with his follow up blood results on January 7th (I'm sorry I don't have full results with details of BUN and Creatinine levels but the vet said they had risen only slightly over the past 6 weeks since the previous test and that the diet appeared to be working for him). Marley seemed to be doing fine until the past 10 days when he lost his appetite a little (still eating, but not finishing his meals). He was still interested in going for walks etc. but my sister decided to have blood tests again just to be safe, and yesterday another blood test revealed BUN and Creatinine levels had doubled over the past 4 weeks since the January results, and the vet has said he now has only up to 1 month left to live.
The vet has advised that he be taken off his Hills K/D diet and that this is replaced with chicken/tuna if he will eat it (which he is doing). I rang the vet this morning on behalf of my sister to ask if carbs should also be included in his diet, and didn't quite understand the response. Initially I was told that that his diet should be protein as a mixture of protein/carbs would be tougher for him to digest. I got the impression that they didn't think that carbs were important. However, when I responded that we were just checking to make sure we were doing the right thing and we would continue with the protein diet and not mix in carbs if it was too much for him to handle, they replied that we should give him a small amount of carbs (something bland like rice or potato) to help him maintain his weight and could probably continue on a diet of protein only for 2 days and then a mixture of protein & carbs on the third day.
This seems to go against everything I've read about diet for dogs in renal failure where the advice seems to be a diet low in protein and phosperous, but I'm not an expert and since Marley seems to have so little time left, perhaps the vet is more concerned that he continues to eat and therefore the poultry/fish is a tastier option for him.
What advice would you give re. care and diet of a dog in final stage renal failure?
Thanks
Sharon