It's amusing that this kind of line is lame until you get confident enough to say it jokingly, and then it becomes a funny one. But until then I highly advice against it, heh.
As for conversation openers... well, just asking opinion over something trivial (and I insist, something trivial) works well, like the name of a recently adopted cat or something. Even if it's bullshit, just say it's for a fried who can't decide or whatever. Then use what they say to you to fork the conversation and keep going. A good idea is to start by telling people you won't bother them long (ie you've got something to do elsewhere), so they don't immediately label you as "annoying person". If the conversation is doing well, you can then ignore this, if it doesn't go well, you have an exit door all ready. If they remind you about it, try to guess if they say so because they want you to stay or go. If it's stay, say you have a change of plans, that it can wait or whatever. If it's go, just go.
>occasional Touhou related stuff (playing the games, archiving story threads, etc.), and trying to squeeze in a round of TF2 every so often
By the way, this is "free time". Especially the touhou archiving, seriously. I really don't see why you think it's not.