Reading the description and thinking outside the box a bit, I think one could also launch the supplied "nightmode.sh" script via the filemon patch; all that would be needed would be the addition of a new PNG for NightMode, followed by the addition of a new script similar to
Code:
$root/.kobo/fmon/fmon $root/nightmode.png $root/.kobo/nightmode.sh >> $root/.kobo/fmon/fmon.log.txt 2>&1 &