No doubt, the single toughest thing I faced in dealing with stopping drinking was friends that still drank. Here are my thoughts on the subject, some based on personal experience.
#1. Saying you have liver issues will work, of course. But you are faced with telling that same story week after week. Even if you don't know them outside of golf, they will want to know if it is a serious issue, treatment you may be taking etc. Also, be sure you know what good/bad numbers are. They may have concerns about the same thing, and want to know specifics. I personally wouldn't want to deal with all that.
#2 Saying you feel bad will work for tomorrow, but there's next Friday, and so on.
#3. Saying you just decided to quit will work, and is the truth. But be prepared to answer why. You will be asked, just the nature of people.
#4. I never said that, always felt it would make people treat me different. I didn't want that. I just wanted them to know I was a person who wanted to stop drinking.
What might work for you (I did this) is to say you really tied one on, and still have a hangover, don't want to look at the stuff today. Then build on that. Next time, say how great it feels waking up without a hangover, and don't really miss the stuff. Yes, you will get some pressure to drink. But it will stop. And you will be surprised how soon someone remarks, "Wow, you're doing great with your drinking. Wish I cold slow down" First time that happened to my, I was stunned.