To try and unlock the pipelines using Rivatuner:
1. On the main tab, click on the button with a triangle on it with the word customize... in front of it.
2. Click on the video card icon and then click on the nvstrap tab and click the install button located at the bottom of the screen.
3. Click and check the boxes that say, "allow enabling hardware masked units" and, "unlock professional capabilities"
4. Click on the active pixel/vertex units configuration and change it to custom.
5. Click on the customize button that is no longer grayed out.
6. You will see a table. Simply click on the table where the missing check mark is for your masked pipelines.
7. Restart. (you may have to restart at other steps in this process too)