For the GPU to activate transcode a monitor needs to be connected to it, copyright or something? (maybe I am not being 100% correct here, as It is on but for some reason you can't access it without a monitor or virtu.. probably a device context or something is needed)
When the monitor is connected then programs like TMPGEnc will show Intel SDK Hardware as an option in some of the Preferences.
Maybe the software Lucid Virtu will also let you without a second monitor, but I did not like having it installed. So not sure how well it would work with third party software.