I don't know about an out and out lie. I'm in euphemism mode right now. "I'm trying to lay off it a bit" or "I'm trying to be good, right now"
An old friend called me up Saturday night around 1 am and asked if I wanted to meet for drinks. I said "I'd love to see you, but I'm trying to be good, right now." She's a heavy drinker too, and we've shared war stories so she must have just "got it".
Without even a pause she said, "okay, then let's just meet for lunch sometime soon." Love that girl! (not an ex, just a drinking buddy from back in the day)