How to include / import by reference structured (DITA) content in an unstructured document?

I've been tasked with finding how to include / import by reference / text-inset / etc.  unstructured (DTIA) content (such as field help descriptions) in a larger unstructured document (such as in a user guide chapter).  Someone I work with said they saw an Adobe representative demonstrate this capability. I know it would make more sense to move everything into structured FrameMaker, but that's not the question I'm being asked... So far I do not see a way to do this, although I do see a way to bring unstructured content into a structured document. 
I would like to find out how to do this (or find out that it is not possible). Any help would be very much appreciated.