Okay if you have the pkill command then it is easy to do. Just right a script like this called xscreensaver_off. Open your favoraite text editor and enter this.
Once saved it will need to be executable. This can be done two ways. In a terminal screen issue he command ' chmod + xscreensaver_off '. Or in the gui if using kde then right click the script and check the box in permissions to make it executable.
But guessing root has control of pkill to kill xscreensaver you will either need to make pkill usable to you by changing ownership of the command pkill. Or it can be added to your sudoers file. Little harder to do that way.
Let me know how it goes.