Steve gave you some good recommendations about patching the holes. It is a good idea to use the backer piece to help support the patch material, if you can finagle such backers through the holes. Where there is a will there is a way, so I am sure you can figure out some way to get a backer piece inside the block.
Now, my curiosity demands that I ask you HOW did you get so many holes in those cinder blocks? Do you live in a "drive by" neighborhood???