Reshoot so the entire scene is properly exposed.
I visited that link today and tried Ann's technique and it worked perfectly. None of her images are showing up however, they seem to be dead.
Bill Hunt also tried to access them and he got the same error when trying to view them.
With that said though, I got Ann's way of doing it to work, and it worked amazinly well. I was able to blend 2 videos together, one I turned up the brightness and contrast on, and the other I left along, and combined them. You cannot tell where video A blends into video B. It's perfect !
A great technique, which when not practiced enough, gets forgotten.
There's a similar thread here:
Ann describes how to isolate an area in Premiere Pro, and then I suggest how to do it in After Effects.