You can use paint stripper if you are quick. I used to do that kind of thing a lot removing graffiti from buildings and other structures.
The epoxy is strong and relatively thick, the overspray is weak and very thin. If the reducer or Xylene does not work use a strong paint stripper, make sure it is water based so it can be washed off easily and dissolve it quickly and remove it quickly.
The way to do it is to have a bucket of water, a broom with natural bristles, not nylon or synthetic, as fine as possible, a big paintbrush and the stripper and a wet vac.
Apply the stripper to a 2 sq.ft area very quickly as thinly as possible, rubbing it to get all the over spray dissolved, apply water on the broom and rub it in quickly, wet vac quickly, apply more water and wet vac again. Then do the next section.
The thin over spray will be removed before the stripper can begin to get into the epoxy, but do not leave any stripper behind. After washing, the stripper solvent will quickly evaporate from the epoxy before getting into it.
Not recommended for non risktakers, but you asked.