Mesh Block Def -> linked Instance -> GH Mesh

OK, so I ask again:

How do I - with C# - reconstruct a valid Mesh object in Grasshopper based on a linked (mesh) Block Instance from Rhino Document which was defined in another Rhino file?

So far I have gotten only so far, but I have failed to instantiate the InstanceObject (or its InstanceReferenceGeometry):

I simply cannot find a way to instantiate a copy of this indirection of a definition.

bild

Manually I can assign a GH Mesh parameter by setting the option “Mode = Copy” and pick the linked Mesh instance in Rhino, which makes the Mesh parameter internalized.
bild

But I don’t want to internalize/store a huge Mesh in the definition (takes forever to save).

I would be fine with just a runtime copy (I extract the parts I need from the mesh downstreams the GH graph anyway). But how instantiate with C#?

// Rolf