Cobbing around objects?

Looks like we are going to buy a junker home (permit reasons) and replace walls with cob. When you cob around objects what do you do to not crush the objects? Like an hvac duct. Lay plank of wood across the top? Or, with electrical, tub with just electrical conduit or would a larger pvc tube be a better option? Or, what?

If your cobbing around objects there really is no need to prevent crushing. If you cob around an object and allow the cob to harden before additional layers it will create a natural pocket. When you build a rocket mass heater you bury ductwork in cob with no difficulty.

What about cracking? Although, I think I can answer my own question now. With enough sand especially, in the mix, there shouldn't be enough shrinkage to cause cracks, even around an object.