-Hide the text/chat/spam when recording so people only don't get distracted from what you want to show them. You should be able to find a command such as hudchatposition to move it off the screen when replaying demos.
-Maybe try get a bit more exciting gameplay to demonstrate.
You could also use the in-game command /record (/stoprecord to stop)
That records a demo and it uses very little amount of memory, then when you need to, view the demos that you liked and use your recording software to record.. there will be no scoreboard or chat popping up. :)
I record a demo of the game using the command / record on the game console, then I open the demo using the CoD4Player and record the video with the X-fire. When I finish recording the videos that I need I edit the videos using Vegas Movie Studio Platinum 9.0.