Unless they have changed live stream in the last few months, you should be able auto upload the stream no matter how long it is...I have a several 3+ hour streams on my livestream with no problems and no monthly fee.
So, while i agree with your overall theme.. You're not loading the whole mesh with Nanite - It's streaming in the appropriate level of detail based on screen coverage for the clusters you can see
You could try going into the INI file and editing the texture streaming settings so that they don't stream out as much. Here's some info: http://udn.epicgames.com/Three/TextureStreaming.html or you can run the game with the texture streaming turned off. Just add these flags to your game shortcut: -MAXQUALITYMODE…