Make a GUI that only lets you see things near your units... or something else to simulate "the fog of war".
Potential prob: will be hard to enforce this - presumably someone would only use a fog option if they *trusted* their opponents to do likewise.
This can be extended to cover other things (???), like not disclosing private information like alliances and stuff that the MasterSimulation knows but the SlaveSimulations needn't.
Of course when you start giving the Slaves less information than the Masters, it becomes harder to make sure that both simulations remain identical/synchronized without transferring a huge load of (otherwise redundant because calculable) data (e.g. basic movement co-ords).
This seems hard. I don't think it's a version 1 feature. Setting resolution to Later.