The docs explain that you can use the Static Pages for Center blocks, but not how. What text do I put in the static page to get a block to show up there?
Some people do read the docs! You miss intepret the "Center blocks." It simply mean you can put the staticpages in the center and in stead of taking the whole page you can set it at the top, after the feature, or at the bottom. That's all it means, and you seem to have done it.
As I said, the code is for the topic. If you want blocks other than the Portal Blocks to show in the staticpages, you need to do it differently based on the type of the block you are trying to move. Not all blocks are the same.
For example, if you want the sections block in the middle, just create the html links. Simple.