You gotta have a friend with you for this one... Make sure your buddy is visible in the background. Go up to the chick and say...
"Don't hate me for asking, but about how much do you weigh?"
Chick gets a bit pissed, but still says "Why?"
"My buddy(buds) over there is(are) daring me to pick you up. I figure I have a better chance at carrying you over to the bar and buying you a drink than the version of 'pick up' that he(they) have in mind..."
Gets one of three things. 1.) slapped. 2.) drink thrown in face. or 3.) get to go buy her a drink. Two of those three get you alcohol. And if you get slapped, you can usualy make you friend(s) buy you a beer. So you get to drink booze any way.