Modify an existing opengl application to render to a PBO (and from there to a file)?

Question

I want to modify an existing OpenGL application to render to a PBO and then read the PBO to generate an encoded video of what was originally going to be rendered to the screen. Since performance is key, I cannot stall the pipeline by doing glReadPixels from the backbuffer as I was doing. I am wondering if there is a simple or straightforward way to redirect everything rendered to the framebuffer and make it instead go to the PBO. In other words, I don't care if it is not shown on the screen. As a matter of fact, I would prefer if nothing is shown to the screen.