Great question!
First instinct would be to add a ConDoc Tag, ELEMENT_Iso Diagram. Draw/model the diagram right in place with your model. Group it. Tag it.
You will need to create another perspective drawing using the Configurator. Only tag turned on would be ELEMENT_Iso Diagram. No need to assign levels or any other tags. Keep it simple.
I worked up a quick prototype you can download here. Keep in mind that if you have already created scenes using the ARCHITECT drawing set, then load this one, it will add a new ELEMENT_Iso Diagram tag. The default behavior for new tags is to be visible in existing scenes, so you may need to go back and turn the new tag off and update a few scenes. Should not be a big deal though, just a heads up!
Let me know how it goes!