How about some alpines that tolerate shade? Maybe something like Saxifraga 'Whitehill'; label states "...cool sun to part shade". Have you tried Sedum laxum? I noticed mine is in shade probably all day. It is shaded by tall plants in front of it and then my neighbors' trees in the afternoon. I think little rock gardens in each container with appropriate alpines would work. Just need to figure out which ones will work with the shade.