Adding ducts to unconditioned attic

[zekk828]

Is it possible to add ducts to a location outside the conditioned space (e.g., attic) by somehow:
-Adding a small amount of air exchange (duct leakage) when space-conditioning is called for
-Accounting for duct (and insulation) surface temperature, which would be dependent on space-conditioning schedule

Essentially, I want to account for the heat/coolth and additional moisture added to the attic from these ducts.

I could create rectangular ducts in SketchUp if necessary, but this would still not address the schedule of space-conditioning or conditions within the ducts. Do I have to run the simulation and then use the outputs of the HVAC runtime to create this new schedule? Any simplified methods?