Cat with gum disease

My friend has a cat with gum disease. She has had it a long time and it won't clear up even with vet treatment. The kitty is always depressed acting and I told my friend I might be able to help her with it if I could find a protocol for her to try.

Any suggestions? I have been toying with the idea of making a spray to have her spray on the cat's gums. I don't think the cat will drink MMS and if it did, it wouldn't necessarily coat all the gums, but I thought spraying all the gums might be better.

I use a CDS spray - 3000ppm diluted 3ml/30ml distilled water.
I spray my mouth and nose several (many) times a day as I had cancer removed from my tongue coming up 5 years ago (before I realized the true potential of MMS). The 4 oz spray bottle lasts ~ a week without refrigeration (no sun light). It is practically tasteless and doesn't sting
We also use it on a myriad of pet afflictions (gooey eyes, sore paws, minor cuts and scrapes etc)
So it would be all down to the personality of the cat - will it take you fingers off rather undergo the indignity of allowing treatment