That would be a bug with the KoboTouch driver, please report it at
https://bugs.launchpad.net/calibre so it can get fixed.
As a workaround, if you use my driver to hyphenate the book (disable the extended features) that will add a CSS file and reference it properly in all the content files, which will give davidfor's code a CSS file to append to. If you disable the extended features in my driver, you get a standard ePub and not a KePub sent to your device.