Assigning boundary conditions to an arbitrary object

Hello,
I wanted to simulate a case where inside my simulation volume i have a sphere which has absorbing boundary conditions.
Additionally i still want to keep the planes defined before for the boundary conditions.
I tried to drag and drop the sphere but it doesn't work.
Is such simulation case possible ?

I don't think the built-in absorbing boundary conditions can deal with anything else than the 6 faces of the computational domain.

I suppose you would have to create your own sphere-shaped absorber, but I don't really know how that can be done. Perhaps by having a series of nested spheres with different radii and cleverly chosen conductivity? Surely there is something in the literature on this topic.

I think that it would not be possible since you can only assign conductivity values for the voxels. Not the edges of the yee cell where the E-fields are computed. This basically means the absorbing boundary gets avaraged and won't work as you would want.