The frame lines will be crucial, so good communication with DoP. How about hanging some blankets off-camera? You can go wild treating the space, but how much of that will be practical?
p.s. can you treat the floor?
As georgi said, knowing the frame will be (and actually always is) very important. Being able to get the mic even just 1 foot closer will be a noticeable improvement.
As for sound blankets/baffles, it depends on the space. If it's huge and open, then putting up baffles and keeping them out of shot might be too much effort for minimal gains. One thing you ...
My answer falls under the category of "fix it in post". If all else fails (and I do hope you exercise all options during production), then UNVEIL from Zynaptiq absolutely works miracles.
Another "fix it in post" solution is this box, which IMHO is nothing short of straight-up voodoo and black magic: