The code simulating a physical universe doesn’t need to make any reference to which brain or camera in the simulation is being “read off” to provide the sensory input stream. The additional code takes the simulation, which is a complete picture of the world according to the laws of physics as they are seen by the creatures in the simulation, and outputs a sensory stream. This function is directly analogous to what dualist/epiphenomenalist philosopher of mind David Chalmers calls “psychophysical laws.”
I don’t know if this insight is originally yours or not, but thank you for it. It’s like you just gave me a piece of the puzzle I was missing (even if I still don’t know where it fits).