I assume the main laptop is a Windows PC (PowerPoint Presentation).
You will likely have to tweak this since I only did this myself for "spitz-n-giggles" - not that I really needed it for anything so I did not explore it to great depth. But I wanted to see if i could use another PC (any PC actually, but Rpi2 in my case) as a second monitor.
1) Installed TightVNC on a Windows PC.
2) Created a fake virtual second monitor in the main PC (In Windows 7, in the Display settings I clicked "Detect Monitors", and since my laptop has an unused VGA plug, that display came up as a "ghost" monitor - so I selected the VGA in the pulldown menu and extended my screen to it as a second monitor. Depending on your version of Windows, you may have to Google "Virtual monitor in Windows 8 or 10 or whatever and see how to do it. Worst case, you can do this:
http://www.overclock.net/t/384733/the-3 ... dummy-plug
3) In Windows, I ran TightVNC Server as an app (not a service, though I think you could do that too), then I made a batch file that ran the commands
cd "\Program Files\TightVNC"
tvnserver -controlapp -sharedisplay 2
to export only the 2nd virtual monitor.
4) On the Raspberry Pi I installed Remmina. Then set up a VNC client connection to my Windows PC. When it connects, it sees only the 2nd virtual screen that is exported from my PC. You then expand the Remmina client to full screen size to get rid of the menus/borders of Remmina. Then you put whatever Windows software you want on the RPi remote screen and run it. (Not video though - too slow for that.)
You will have to set the Windows 2nd virtual monitor to a proper screen size before you connect from the RPi to get the look right (probably trial-and-error a few times).
That's probably most of it. I'm sure you can overcome whatever obstacles there are in your specific setup.