This one is a bit riskier than most - if you mess it up, your Kobo won't start up and can't even be factory reset. To be safe you have to open your Kobo up to back up the microSD card before doing this in case something goes wrong, so it's not exactly trivial. There's no guarantee you won't break the Kobo's bezel while opening it up to back up the SD card. Of course, anything like this is likely to void your warranty, so if you mess up you'll be on on your own.
It's fun, though.
How to change your Kobo's boot-up screen
(an improvement to the Kobo's upgrade scripts that checked the maximum length of the boot splash image would make this process a lot safer. Right now, it just writes whatever you give it, and if that happens to overwrite the kernel image later in memory ... whoops!).