Walk past a 3 set, stop, turn and say, "Woah, you guys are just like Charlie's Angels... (To center girl:) You're like the Alpha-girl leader, (to left:) you're like the really cute one that knows all about guns and flies the chopper and (to right:) you're the other cute one with that bad attitude that does the computer hacking and blows shit up. Come on, do the pose!"
Then i direct them into something like the famous Charlie's Angels pose w/ fake guns drawn and tell them they could be on a T-shirt.
It works best if you combine this with somewhat believable cold reads stuff like you're the bad girl, you're the fashionable one, you're the hot little Asian, you're the one in leather pants, etc.