Fl00die, it's not impossible, but depending on your physical build and how easy it is to access stuff, if might be more trouble than it's worth. If you unplug your USB gamepads, for example, you will probably have to deal with Windows ID reassignment, which means reprogramming, which means you'll need to access Windows, etc, etc. You have to ask yourself if you really want to hassle with extra programs or finding hardware for something you're not going to use a whole lot. Again, it's not impossible, but it's not without issues, especially if you envision those same gamepads functioning as P3 and P4 as well.
Mirroring the video seems like the easiest way to go for spectators, as they'll see the games as they're being played.