I've never seen them do anything like that for ebooks.
About the only "discount" I've been able to get off of Amazon prices lately was the eBillMe (I think that is what it is called) offer where you buy $100 worth of gift cards and you get $15. I've bought the $100 of gc and I've sent in my papers for the $15 but it has a long processing time.
This is it ......
http://www.ebillme.com/gift-cards/amazon/promo