As for the white cranberry juice, it was easier for me to fake it since I was hosting... I could sneak off in the kitchen and fill up my glass. But if you are out at a party and there is a bartender, I've heard of people telling the bartender at the beginning of the night to just keep slipping them virgin drinks.
Another time I was at a Christmas party at a friend's house and I would just nurse the same glass of wine most of the night. I'd put my wine glass to my lips occasionally but not sip any. If anyone asked why I wasn't drinking much I'd just say that I had way too much the night before with so and so...Then when no one was around to see, my husband would take a big sip of my wine.