How long has he been on the pred? In dogs, anyway, pred really seems to stimulate their appetite--and can be used to treat IBD and as 'quality of life' drug for cancer. It might be all you need to get him back on track. So I'd still assist his feeding for at least long enough for the pred to have some effect...
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."