Nope I have tried so many combos of keys and nothing so far :( The man that uploaded the video said he used an "exploit" that Bohemia didn't think about in order to gain access to the 3D editor so now im lost :(
I used the 3D editor in arma 2 because it was extremely helpful for me to place objects accurately next to buildings etc. because im sure you're aware the Grey'd out rectangles and squares that represent buildings in the 2D editor definitely don't correspond to the actual objects size and shape. So previewing everytime you make a change to a placement is a F*ing pain the in the bum haha.