I have a fourteen and a half year old bitch who has been on prednisolone for about a year now. She was a bit unsound, and her skin was breaking out in sore patches.
She was prescirbed one a day, but I have now got it down to one every day and a half, I tried every other day but the sores started to return.
She does drink a fair bit, and is a gannet where food is concerned, but in herself she is fine. Like your boy, there is no real long term to have to worry about, so I would go for giving him a better quality of life while you can.