In dual gaming mode it should be possible to watch 2 different movies at the same time:
1- Use a video editing software to create a top/bottom 1080p mkv with diferent videos on top and bottom part (doing all the scaling needed).
2-Mux both audio streams in the file.
3-Play the movie in dual gaming mode and the left player should be able to watch movie 1 and the right player would watch movie 2 (sound should be available only from movie 1).

If the file is played via HDMI from a computer there should be a way to send audio 1 to hdmi and audio 2 to headphones.

Of, course its a pain to do all de encoding but anyone tried it?

It might be possible to implement a system to do that on the fly. Maybe with some filters in ffdshow, or maybe in the tv itself with different hdmi inputs... Well, just ideias!