The next generation of base stations and tracked devices won't have this problem, because the base station ID will be encoded in the laser, and a headset can ignore base stations it doesn't recognize. Unfortunately this will require both new base stations and new headsets / controllers, and I've seen no estimate on when the next generation will be released.
In the meantime, the only solution is to find a way to partition your environment so that any given region is only covered by two base stations. It's a pain, but you can cover a large area with a single pair. If you only have 4 people in a confined space you might be able to set up so that you only have one pair of stations. If that's not practical, you might look into mounting barn doors around the stations so that you can restrict their field of view.