Then he will have a huge chunk of desktop that Windows is expanding to that is not visible. Windows will pop up over there that he can't see and headaches will ensue.
The problem is that AMD drivers are pretty crap when it comes to more than one display. Cloning the display, it forces the resolution to the lowest common denominator. That means the 1080p that the receiver reports as it's highest input value. Again, the best solutions have already been found. Surround with 60 pixel bars, or stereo at full resolution.
Nvidia drivers where more flexible at one point, allowing high-res cloning with scaled output to a second display. For example, 1920x1080 could be rendered natively to the primary display, then that could be cloned and scaled to 1280x720 for a second, lower-res display. I don't know if Nvidia still functions that way today, but it has been a feature in the past. Either way, it's a laptop. Your graphics are what they are. Pick between your two available solutions.
And Joe, please start reading posts before responding. He clearly stated from moment one that there was no external display. Then you spent three days telling him how to make that external display work.