If that's a setting where you would normally drink then don't risk it, do something else instead. Maybe go see a movie, or go out of Chinese food or maybe get a massage. If you do something else make sure it's as good or better then the party, just sober. You'll be able to join in time when you have more sobriety under your belt.
Also, I agree with what Foolsgold suggested. I've found that a glass of coke with a lime wedge in my hand is sufficiently booze-y looking to ward off any questions. Really, unless it runs dry, nobody bothers to ask. Apparently non-alkies don't obsess over booze, who would have guessed it?