I believe @Archmage put a feature into EnergyPlus where a zone is allowed on the supply side of AirLoopHVAC. I couldn't find an example file or documentation, but @Archmage or @MJWitte MJWitte can probably point you to some information.

OpenStudio currently forbids a ThermalZone on supply side, but if it is something people need we can certainly open up the API to do this.