there are ways to get outside the eyes of a player, however, I don't know of any way to freely control the camera as if it was a spectator. The closest you could do is use several 3rd person camera commands that will let you move the camera in different positions around the player who recorded the demo.
First turn on cheats (/devmap ffa_yavin)
Then, while in the game, find the camera position you want:
/cg_thirdperson 1 (puts camera outside of player)
/cg_thirdpersonangle ### (puts camera a certain angle around the player, 0-360 degrees)
/cg_thirdpersonrange ### (adjusts distance camera is from player)
/cg_thirdpersonvertoffset ## (adjusts vertical angle of the camera to get an above or below angle on players)
these are the basic third person commands to use when in a duel. The drawback is that, unless you're an experienced scripter, you'd have to set the angles before running the demo and would be limited to that angle for the rest of the demo. Also the camera will always have the player who recorded the demo in the very center of the screen and will follow that players movements and direction. For additional thirdperson commands type /cg_thirdperson into the console and it will list the rest of them.
Your best bet is if you know you're gonna record a duel, have a spectator demo it from whatever angle you'd like.
Hope this helps.