In Blogger, we can easily insert “Read More” section by clicking on the "split post" button from the toolbar
or by adding the HTML tag in the source code:
In earlier versions of Windows Live Writer, there is no split post feature. But manually adding the read more code in the HTML source code may be tedious. Instead you can download this plug-in in<!--more—>
Windows Live Writer. A button will appear in Windows Live Writer and it can be easily access from the menu.
Download the Windows Live Writer Blogger Excerpt (read more) plugin from “Scott’s SkyDrive”. Look for a file by the name “InsertBloggerExcerpt”.
Where to install the plugin?Copy and paste the plugin at:
c:\Program Files\Windows Live\Writer\Plugins
or “c:\Program Files (x86)\Windows Live\Writer\Plugins ” if on x64 systems.
You will see a Blogger Excerpt tool added after the plugin install (see indicated in red).
On Windows Live Writer 2012, "split post" is included (see indicated in green) so there is no need of the plugin anymore.
Link shared to Scott’s Skydrive has a few other Windows Live Writer plugins which you may try also.