I generally just run conduit down the wall and mount the boxes on the surface. It really doesn't look all that bad, and sure beats the heck out of trying to cut cinder block 3/4"-1" behind the surface of the wall and through an opening the size of a single-gang box. And once you factor in the time it takes to fish wire through the block - IF the block isnt' filled with concrete - installing the conduit is much more cost effective.
Kevin
