disable USB charge on laptop

Is there a setting somewhere either in the phone or in windows XP where I can disable the feature to charge the phone when it is plugged into a computer USB port? I�ve got a few users who have a blackberry Tour 9630 and they have laptops. Yes the drain on the laptop battery is small but does anyone know how to disable it?

I think you can turn off power to the usb ports under Device Manager and then the ports' various properties. I'm not sure if this also disables the usb port from being able to transfer data.

Why not just unplug the phone?