It's weird but occasionally I will roleplay and pretend to be a soul that has taken over their body (When I really haven't because it's just their view) but I don't know how to... Say, un-possess them.
In creative. You can go into /gm 3 (spectator) and click on a person to view what they're seeing. However, I haven't discovered how to leave the player's view and keep playing as yourself.