OMG! I'm so sorry for you. I have never dealt with it, but my husband and I both had pneumonia this winter and food does seem disgusting at first. I presume you are giving antibiotics, so as long as he is drinking and keeping warm, and, of course he has to be encouraged to move to stimulate his lungs to clear, I'm sure he'll get better.
I suspect that if you offered chicken broth with small bits of chicken in it, or a hamburger gravy thinned out, more gravy than meat at first, then bulk it up with a little bit of rice, you might tempt him. When our Beagle was sick we'd lay on the floor with him, holding his head up on our legs and we'd dip our fingers in something savoury and have him lick it off. At first we had to rub it on his gums, but eventually he'd lick and get more and more interested. Pneumonia makes you very tired and lethargic and seeming disconnected with people around you, but he will want you near for comfort, maybe even for warmth.
What type of pneumonia is it? Bacterial or Aspiration? If it is aspiration, did they try to suck his airways clear of the foreign matter causing the infection? If bacterial, did the doctor prescribe a good antibiotic? Have you Googled it for what you can do at home to help him feel better. I found a lot of websites with everything from organic/holistic treatments to general/standard medicine care.
I'm hoping and praying for you!