Open the Project Properties Window
Use one of the listed methods to Open the Project Properties window.
All projects contain at least one configuration called default. You can see this on the left side of the Project Properties window as the second node in the tree. All items collected as branches below this node are part of the default configuration.
Click on the Manage Configurations button at the bottom-left corner of the Project Properties window.
Duplicate Existing or Create New Configuration
Give it a Name
The name you provide here is what will be displayed in the IDE to identify this particular configuration in places like the Project Properties window and the drop-down box on the main tool bar.
No spaces are allowed in the name. If you put them in, the IDE will automatically remove them.
Click OK when done.
You should now see two configurations in the tree on the left side of the Project Properties window. Their names should be the same as what you provided in steps 5 and 7 above. Each one of these may now be configured separately, effectively making them "projects within a project".
You can repeat this process as many times as you like to create any number of configurations within a single project. Obviously the developers have imposed some upper limit on the number of configurations - but so far no one has hit that limit, whatever it is.