Just take the drinks offered and tip them out later, in the garden, toilet etc.....
If you dont say anything, then nothing can be taken the wrong way or seen as a "lie"...

Keeping quite is usually the best way to lie.. I had wine poured at chrissy, sipped it, and it went down the loo whenever I went so noone noticed or said anything..I think I wasted a fair bit!!!
making up a lie, or it being a big deal, usually brings about suspicion!!!