There is no setting in any config file to turn it off permanently. The only thing you can do is turn the screensaver off along with all other light and power saving settings until you next suspend and resume, using the following command:
qcop QPE/System 'setScreenSaverIntervals(int,int,int)' 0 0 0
Everything can be set back to how it was without a suspend/resume with the following command:
qcop QPE/System 'setScreenSaverIntervals(int,int,int)' -1 -1 -1