I hate retrofit in cinder block or even worse in concrete The most versatile is to cut the top blocks vertically until you get past the bond and down to the hollow part and install emt and steel flexible conduit to get down the blocks to the switch. Use a masonry box and a lot of mortar to fill the cut and set the box. Stuff a bug wad of metal screen in the block that the switch occupies to hold the cement or mortar from falling down the wall. You might want to ask the building inspector or a structural engineer what parts of the bond you should avoid but I am sure it is possible to cut it vertically for the depth of 2 or 3 inches you would need to get the emt through. I have done too many of these and that is what i did with Building inspection approval. The ceiling is surface if there is not void above. If you should decide on BX or any aluminum raceway you need to be sure there are no chloride additives in the cement or you will need to protect the armour with tar heavy tape etc.
