I don't know if anyone has mentioned this, but did you know that Ebates works for Kobo books? (and devices!) You just can't buy them through your device. On the PC, log into Ebates, then go to Kobo from their website to shop (or use the extension). If I'm not near my computer, I do this with the Ebates app on my phone. Then sync your reader and the book will appear there, and in a bit you'll get a message that you got a rebate.
The rebate is 5%, so not a lot but it does add up if you buy a lot of books.
Both companies are owned by Rakuten, that's probably why this is possible.