Neko loved her chicken flavoured compounded buprenorphine. That is, the chicken soup flavour, not the roasted chicken one. Cats!

I got a vial from my local compounding pharmacy and much cheaper than from the vet, about $100 for 3 months worth. The vet needed a special prescription pad to order it as it's a controlled substance. Neko was on it for a couple years because of her acro arthritis, and it was a game changer in how much better she felt.
You also asked yesterday:
I weighed Neko regularly, and fed her according to what weight the vet and I thought was a good weight for her. I also fed raw food, which I found seemed to be more filling than canned food which has more fillers in it. You might want to discuss with your vet whether Max needs to lose weight or not. The acro tumour puts out excess growth hormone, and that can mean muscle as well as bony/soft tissue growth. Think teenage boys. Weight gain may be appropriate if he's getting longer/taller.
The other tool that really helped me was the autofeeder. Once Neko learned the autofeeder fed her meals after PS, she no longer bugged me for food.

One more thing that will really help you is getting Max into better blood sugar numbers. Nice to see yellows a couple days in a row now.