I would suggest you also post this in the Holistic forum as we have veterinarians that understand the natural support of very sick animals and they can more specifically answer your question.
Medically I would support this dog with steroids, pain relief meds, good nutrition and supplements.
Sounds like this is advanced so I hope all your efforts will help him maintain a good quality of life. When the time comes you will know you have done everything for him... and he was very lucky to have YOU.
I agree with all of Dr. Humphries comments. As a traditionally trained, holistic veterinarian, I work with many dogs with Lymphoma quite successfully.
We recommend an anti-cancer diet, which is posted on this site under my Canine Lymphoma blog and also use a natural, patented pet vitamin supplement called Paaws.
At some future point in time, when and if his appetite declines, you may need to add in prednisolone as well.
Our patients with Lymphoma generally enjoy up to 2 quality years of life post diagnosis.
Dr. Carol Osborne, DVM.