Extend Desktop to Monitor over LAN
Solution 1:
A hackish solution would be to extend your desktop to dual X displays on your main machine, with DISPLAY=:0 being your main screen and DISPLAY=:1 being to the right. Run x11vnc to share display 1 and then run a barebones client on the laptop with a VNC viewer that connects to display 1 over Ethernet and projects it full screen.