On official S5 WCA page in cooperation with S50CLX DX Cluster admins prepared a table of DX spots carrying castles reference numbers and an option for sending spots with WCA or SOTA reference number.
Instructions for DX spotting on S5 WCA page:
http://forum.hamradio.si/viewtopic.php?f=64&t=12284
Best 73, de Zvone - S57PZ