You can put a button in a harness without using any section. However, you need to use a Container in your Harness, if you do not wish to use a section. When you create a new Harness, you will get a container in it by default. And you will see some cells in the Harness rule as well. You can drag and drop your buttons into those cells on the Harness form. And then go ahead and configure the button to suit your requirements - a button is now available on the harness without a section.