new trick shared by mdclements, kobo dev, although for a different reason
rename your sideloaded epub books so that they have .kepub.epub as the extention. This will open up KEPUB only options to sideloaded books, such as dictionary and highlights at the current expense of losing your book cover. This also works on at least the wifi version as well for dictionary support.
Also, with Tamings discovery of the Fonts additions (create a fonts directory on the root of your kobo touch's directory and populated it with fonts). This will also become available to sideloaded using the above trick. This however does not work on the wifi.
Thanks mdclements and Taming!
update : word of warning from mdclements:
Originally Posted by mdclements
I would strongly discourage you from renaming your ePubs. Kepub-only functionality will most likely not work on your renamed sideloaded books.
so as with any hack, use at your own risk!