Donles,
I am thinking in terms of two dissimilar materials with a NM wire sandwiched between. As the block and brick expand with temperature changes, the NM is going to be subject to constant rubbing. I think that the wire should be run directly out of the back of the box through the block with a piece of rigid or EMT. It will protect the wire and get it into the inside of the building where it can then be run to the next light. Making it both easily servicable in the future and also giving it a little more protection from natural occurences. This setup would also allow the installer to place the box where they want it and not just where it would end up.
