Although it's not in the format bar, it's still easy to add a "Read More" indicator to your post in Blogo.
Firstly make sure that you have placed the cursor where you want the "Read More" to appear.
Then you can insert it a few different ways:
Click on "Post" in the Menu bar at the top of the screen, and then just select "Insert Read More" from the dropdown list. Alternatively you can use the keyboard shortcut SHIFT + CMD + M.
If you right click where you want it to be placed, you can then just select "Insert Read More".