How to include someone into a scene when they aren't there? In the when photography was still a luxry, people brought the pictures of their deceased families to a set when they were taken family photos by photographers. In this way, they can have those family members in their photos as well.
Similar idea may be applied to cinematography, in the scene, when father and son are discussing the son's future, the deceased mother, who is also an important part of this family, is included by having her photo placed on top of a bookshelf.
Another item to be included is the admission letter from a university, since they are arguing whether they should open and read the letter. Where's the letter? It is placed to where no audience will miss.