Serial communication lost at screensaver

We have a number of laptops used to test components at electrical substations. The testing is done through a serial connection. Because these laptops also connect to our LAN they are covered by our group policy settings which lock the desktop automatically after 15 minutes of inactivity. When this happens the connection to the device is lost and the techs have to start all over again. Anyone have any thoughts on how we can keep the serial connection running when the desktop gets locked? The laptops are Panasonic Toughbooks running Windows XP Pro.

Thanks