Jezuro released this in-game tool in the BI forums.

Quote Jezuro :
Being such a productive community, we thought you might be interested in a simple in-game tool that can help you set up just the right amount of "brown is real" to your missions

I haven't looked around trying to find out if someone didn't write something similar already, so it's quite possible there's a better tool lying around. This is just a simple mission with custom dialogs built in, so don't expect anything too fancy. Feel free to add you own changes though.