Certainly you haven't "hit a dead-end". You can, with some effort of learning write a E+ measure to include your zone humidifier.

You can read about how to write an E+ measure here.

It is good idea to start at the top of the page of the above link to learn about OS measures.

Alternatively you can use the inject IDF object E+ measure from the NREL BCL, which enable you to inject the IDF object , in your case Humidifier:Steam:Gas into your OS model.

Edit: You can look at the example found in the E+ example directory: 5ZoneWaterCooled_GasFiredSteamHumidifier.idf