I'm looking through the 2015 What's New document on Composer, and it says that Render Mode can be a document property, but only if I create an environment variable called DS_3DVC_OVERRIDE_RENDER_MODE. How do I do this?

Here's the full text:

Render Mode

<p style="padding-left: 30px;">You can now define the render mode as a document property, or as a default document property, of the viewport.</p><p style="padding-left: 30px;">You set this definition in the Viewport page of the Document Properties or Default Document Properties dialog box.</p><p style="padding-left: 30px;"><em>You must first create an environment variable, DS_3DVC_OVERRIDE_RENDER_MODE, and set its value to 1.</em></p><p style="padding-left: 30px;">Previously, you could only set the render mode from the Render tab in the ribbon.</p>