Attach drive to mortar without splitting???

One of our downspouts seperated from the house. It was attached with a drive/rack setup that to me never made sense. The existing drive is bent and no longer attaches to the rack properly so I wanted to replace it. I bought a new set but am really afraid to pound it into the mortar. What's the correct way to install this? The drive is smooth and just looks like it wouldn't hold at all even once inserted. What a hokey setup....