Referring to built-in GHAs in project

I wish to be able to use classes defined in some of the assemblies shipping with Grasshopper - like Transform and Vector - in a plug-in I am writing. So far I have not been able to refer to the GHA files directly as references:

I can make a local copy of the GHA, rename it as a DLL, and then add it as a reference set to copy-local=false… but this seems a little clunky to me. Is there a proper way?

That is the proper way I’m afraid, unless you’re willing to use Reflection or dynamic and resolve everything at runtime.