There was plenty of references on the forum (viewtopic.php?f=28&t=30659, viewtopic.php?p=158260#p158260 ...) but I couldn't understand how considering the maps.
The truth is that the maps (http://dmweb.free.fr/files/Hint.Book_Pa ... 9_Scan.jpg, http://dmweb.free.fr/Stuff/3dh/csb/default.htm?1,26,27) are incorrect.
There's a false pit that is not indicated as so at 1,26,27 (according to the CSBuild tool that I have troubles to make work, but that's another thing).

I haven't tested it yet, but one could pick up the corbum from the ros side then quickly step back and step on the right to get on the false pit, and then to the tile on the ku side that closes the pit in front of the ku corbum.