Not sure how useful this is, but Groupon is selling coupons that can be used towards hotel reservations through ikyu.com

5000 yen coupons on sale for 2000 yen, good towards reservations of over 35000 yen:
http://www.groupon.jp/cid/230443

2000 yen coupons on sale for 500 yen, good towards any hotel reservation:
http://www.groupon.jp/cid/230442

You can purchase up to five of each but, sadly, only one coupon can be used per reservation.