Do you have it as a separate Module, or just one separate Controller, or multiple Controllers without any logical separation from Frontend (except for Auth ofcourse), or something else?
Assuming that backend is reasonably complicated, i.e. something more than review/confirm/delete comments for your BLOG.
Definatly belongs in a new module then it is easy to create a separate layout in my opinion.
In a recent project a colleague created a separate admin controller in each module with the layout defined in an admin module. This way he could drop in/remove modules from the project with the main admin module autodetecting which modules are installed and creating menus based on the admin controller found in each pluggable module.
I have explained that poorly, but it’s a good system.