Place a physbone chain somewhere on an avatar, and set its immobile state to "all" and 100%. Place a physbone collider close to it (within ~20 cm), on the same transform on the avatar, so that the chain and collider are siblings, and set the physbone chain to collide with that collider.

One would assume that, if the physbone chain is immobile, and a sibling to its collider, there is no way the two could ever collide without a force pushing the chain against the collider. However, if an avatar moves too much or the framerate is too variable, you can observe that the physbone chain will 'react' as if it were colliding with its otherwise unreachable collider.