Given that the regulations defining the floor define that area as extending between the front and rear axle lines, there is really very little room for adding additional ducting that may divert air into this area; I think it is fair to say that teams are already doing as much as they can in this area.
Case in point : the elaborate splitters that we have seen in recent seasons.
I can't think of any other method for dumping additional air under the floor, but that is probably why I'm not an engineer