The best that I've come up with on these lines was lying that I liked Dragon Age... After that I was pretty much on for some crazy nerdy sexings (seriously, she wore elf ears... I should have stayed in touch really).
Its funny really, because at least a handful of the girls I've slept with were at least as nerdy as I am (most of them being into LARP and cosplay and what have you, and indeed the one I've ended up planning a wedding with spends a lot of her time in a very very long and convulted free-form zombie role playing forum) but I've never really gone the nerdy route with chatting them up... It seemed practically unsporting like putting in the Konami Code on the first level. Frankly if just screaming 'ZOMG YOU PLAY WOW THATS AWESOME' is going to get someone in bed with you then the chances are you aren't going to be the only one who has figured that out, and that means you're going to have to beat the other nerds off with a stick. If anything, going from a less stereotypical route is the way for great success.
It's funny really... I think that all the nerdy girls are well aware that they can easily and immediately bed any of the sweaty mouth breathing crowd and as such (and quite bloody rightly) are looking for something just a little bit more than that even in casual sexing. Its not like nerdy guys are in short supply, so they might as well hold out for one they actually like...