Well, I can not tell you about the usage of variable inside the RoR settings, I can not help more further with this part.
also, I would recommand you, if you need to implement in short time (else wait for @sscarduzio is back to give more information.) , to try my workaround, that I use. see here
and set back your indice as .kibana , and use 2 blocks.
of course, all members belonging to the same group will be able to delete/replace vizu/dashboard, since they will match block.
to prevent this, split users by spliting RoR blocks, with different groups