Yeah, I wound up just creating a new object with DOpusFactory.Map and passing the individual key/values to initialize the new object. Not as concise as being able to copy directly from the env var, but it works.
Something just bugs me about getting a reference to the actual environment variable within the tab. I don't think you should let us write directly to the environment by making a value assignment. Even though you can, I'm still updating the environment var with an explicit Tab.vars.Set() call with the new environment object.