As funny as it sounds, if your interest is martial arts... don't try to pick up girls that are into martial arts, at least not with the intention of looking for a nerdy/geeky type. Self-Defence classes aside, in my personal experience, women that are into martial arts are usually a little... more hardcore, you know what I am saying? Martial arts is more of a men's activity (and combat sports even more so), and women who are really into these type of things tend to feel the need to compete on the guys' level. Now, the only martial arts with a higher geek factor are, in my oppionion, the impractical ones (Kendo, Kenjutsu, Kyudo, most forms of TaiChi* and Kung Fu*), so you might want to go for those.
*Not a generalization of these styles (Kung Fu isn't a style to begin with), but TaiChi ist mostly practiced as a form of meditative physical education rather than real combative application.