An interesting conundrum, this fluffy way of "dealing" with the problem by persuading the person to go sick.
Pilots who turn up to work under the influence almost certainly have a problem, a serious alcohol problem. People without an alcohol problem just don't live like that, and thinking you're doing anyone a kindness (least of all his future passengers) by getting him to declare a cold and go home to get pissed and fly another day is surely a pretty good way of passing the buck to someone else to do a proper job later, hopefully before he scribbles a whole airliner full of people. How would you feel if you'd persuaded him to go home and a month layer he's lying in a field burning with a clear blue flame amongst 200 bodies?
May I suggest this isn't the right way to deal with the problem at all. Send him home by all means and perhaps give him the chance not to be nailed, but there has to be official follow-up or you're partly responsible for any future accident. All airlines should have an abuse programme that is designed to cope with people like this. Use it, or regret it.
Think on it...