Had the same problem with a friend who doesn't have a Playseat. I 3D printed 2 chair stoppers for him from Thingiverse and he is thrilled with them. You just have to scale them a bit as the Hero castors are bigger than normal castors.

I used to have the Playseat, which always shifted. Solution: Cut the tennis ball in half and clamp it under two wheels. But I don't need it anymore with the Hero.

There is no such thing with this chair.