How do I create the portal effect from portal?

So I’ve been trying to figure out how to recreate the portal effect from portal and portal 2 for some time now and I havent seen anyone who has accomplished it create any tutorials. So I got to thinking about a solution to this. How difficult do YOU think it may be to recreate the portal effect by using level streaming and a spawned copy of the player to do this, and have the player copy mimic the players movements opposite to the player? Is it feasible or too difficult to be worth while?