Wow, guys...
The EASIEST way to pull this trick off is a very simple one. Get to the bar a few minutes after your group, or at the very least, make a pit stop while everyone else heads to order. Once they're done and seated, stop by the bar and order a coke WITH A LIME. Tip the bartender (let me repeat: TIP the bartender) and tell him/her that you are not drinking tonight.
Most anyone in a bar who sees a glass of coke with a lime wedge on the side will automatically think, "ahhh, rum and coke".
And for those who steer clear of cola products... club soda actually has no calories and doesn't taste half bad, with a LIME WEDGE!!! (aha!) Again, bar-goers will think, "ahh, gin and tonic/vodka tonic".
Trust me. The "lime-wedge ploy" works like a charm.