Welding physics asset bones at runtime

I’m trying to implement dismemberment, and to do so i set the scale of a hit bone to 0, 0 ,0 but this makes the mesh stretch out, because the bones still have collision. Is there any way to weld the bones of a physics asset at runtime? When i weld in the PHAT it works fine, but i want to weld the bones only when a specific bone is hit, otherwise they should move freely. I think this is possible with body instance, but im not sure how to use it.

I seem to have fixed this problem by setting the constraints of the physics asset to use projection with an tolerance set to 0. So if anyone is looking for a workaround for a similar problem this is the solution instead of welding bones.