I could throw some shielding behind it to catch anything tryong to go out towards the parking lot. So far, I've simply stuck to keeping my configuration nice and tight. I have since upgraded from a 54gs to a 350n router too though I'm still sticking to 11g/wpa for now.

I hadn't considered reflecting the signal though, maybe a reflective shield on the shelf under the router to bounce everything upward would have some effect.