Okay heres what you do. You buy a laptop with a good wireless card. Go back to the office at 12:00 at night .... Unless you work at night ... then go at 12:00 in the day. Take out your best pair of glass cutters and jump through the window. Run as fast as you can and hide under his desk. Flick on his wireless modem. Turn on your laptop scan for the connection. Once your on. Steal the files. The run to the monkey driving the getaway van.
(But in all seriousness even if you could get the signal chances are you would need his wpa key. and if thats the case your out of luck)