I have a suggestion....If you really must go....and aren't ready to "tell" them...
Maybe you could be the designated driver? Maybe you could be the one who watches out for the other gals? Maybe you could hold their hair back while they puke in the bushes
??
If I was in your shoes, I would tell them I'm not gonna drink ladies, I'm gonna watch out for you all, I'll get you home safetly!!
Just a thought...good luck and please consider what could actually happen if you drink?!