I think we can be reasonably certain that the elder Fischer was simply a construct of the third-level dream maze created by Ariadne, essentially the prize at the centre. None of the other character actors are available to play him and he's already locked inside the hospital/vault when Fischer Jr and Eames arrive at the tower.
We know from the persistent presence of Mal, courtesy of Cobb's mucked up psyche, that as well as creating physical locations and obstacles such as guards, it's perfectly possible to create projected characters, something that's backed up by this deleted scene from the screenplay (during the 'planning the heist' scene)
Two AFRICAN PEDESTRIANS wander into view.
ARTHUR: Are those yours?
Eames shakes his head. Cobb turns to Yusuf.
ARTHUR: Yusuf?
YUSUF: Yup. Sorry.
COBB: Suppress them. We don’t bring our own projections into the dream—we let Fischer’s subconscious supply the people.