You can actually place weapons and items out of your own reach.
So I called myself being extra sneaky by putting my weapon underneath the couch in Silvo's room.
That way I could come in unarmed and walk in the room behind the couch and kill him, easy.
Only problem is that I placed it too far under the couch and wasn't able to get it again. I was very upset did all that planning and all the effort to complete the challenge and then to fail it cause I couldn't get my weapon from under the couch...