This would be pretty neat, but I kind of already have a way to do this without the chat box or any text on the screen. :3
If chu make a movie on FH, if you type what you are going to say into the box (So your char will lip sync it) but before the actual text, press enter a few times so when you preview the movie, the text will be off the screen yet it will still lip sync. Aka, you press enter so many times that it pushes the text off the screen. X3
That would still be really cool, and helpful to those that like to make videos and such a lot though. :o