When DJ get's grabbed/up thrown he just starts making a dash-dancing motion really fast and hopes to smash DI out. It's pretty hard to do it with fox, but it's really easy with peach/sheik/marth, at least I think so.
The Doug has been doing this for more than a year, because someone I forgot (CJ or Azen or the like) taught it to him at FC3.
So this method to almost always get a smash DI has been out there for a long time but really not widely known.
If you do a dash dancing motion you'll likely do 1 smash DI during the few hitlag frames.
You have to do it as fast as you can and with a movement as wide as you can in order to get more efficiency. It's very noisy (that's how I noticed Doug doing it)
I don't think anyone can input 2 opposite smash DIs this way because it's hard to maintain a dash-dance motion at an extreme speed.