Can you attach your device to your machine as an additional display. For example with Windows you can use a programs like spacedesk and attache devices ase and additional display via a network connection. However Spacedesk does not support devices with displays with may pixels like a 4K display. I have attached my Surface pro 3 and my android Samsung galaxy 8.4. Here you see my galaxy 8.4 2660x 1600 sitting one my surface pro 3 connected to my workstation as a third display.
Thanks for the reply! I'll try to find some way of doing this on my iMac!