On-screen + texture drawbuffers possible?

Is it possible to render to the screen and a (color) texture at the same time or do I really have to:

a) Setup a FBO with 2 color attached textures and when I’m done rendering render the first texture to the screen.

b) Render to the screen + aux buffer and after that do a copyteximage or similar of the aux buffer to a texture.

(meaning that I one way or another would have to do an extra fullscreen fill)