How can I stop XScreenSaver from waking up on Mouse Input?

Using xscreensaver you can adjust the number of pixels that the mouse must move before deactivating the screensaver; not sure about completely disabling the mouse though.

If you are not already using XScreenSaver within KDE you can follow these instructions to set it up.

Once you do that you can create a file in your home directory called .xscreensaver and in that file enter:

xscreensaver.pointerHysteresis: 20

With 20 being the number of pixels (10 is the default).