Have a look at the ScrollView examples summary there you find examples on how to populate a ScrollView.
If you have a lot of Buttons it would probably be easier to add them in the code.
In the Designer you can define a Panel that could be higher than the screen and add the Views.
And load the layout file to the ScrollView.Panel
You will need 2 layouts, one, containing the scrollview which will be loaded to the activity and the other layout that will be loaded to the scrollview, take a look at the attached project.