This code should work on a page by page basis for custom pages you add inheriting "BlogBasePage", but for BE generated pages you would need a different approach.
The way I do it for BE pages is to use page detection in the master.cs (not unlike the code snippet you have at the start of this thread).
If it's a BE page then alter the layout (giving a blanket layout change for all BE pages) and then add HTML to individual pages to structure as required.
The tinymce editor has a button that you can use to add code snippets (HTML templates), but does require configuring, alternatively just drop the code into the editor in HTML mode. I'm using BE pages exclusively and find this works well,
have a look and click around.
If you want a hand setting that up, you're welcome.