Here are some ideas. First, ask her "Oh, do you like (name of game)" or "do you like games like that?" That gives her the ability to tell you up front if she has a man. If she says she does, then you mention you were looking for the same game and talk to her about it. At some point, prefereably before she goes to pay (since it's akward to follow a girl around if you haven't engaged her interests yet), though it's rather difficult in game stores these days unless you're talking about used games, you meantion it's a damn shame there's only the one copy available and, should you get good vibes, say something to the effect of "maybe I can come over and play with you once you've had some time with the game."
Talking to women isn't difficult or dangerous, and should not be avoided when possible. The more it's done, the easier it gets, after all. And aside from actually trying to pick the hottie up you have no recourse. You can't steal the game from her, and you shouldn't try to talk her out of buying something just because you want it. But if she's single, god dammit that's gotta be a sign! :p
You do not have the right to never be offended.
