It technically is possible... but would take alot of work and would be a bit glitchy.
What I was thinking was that you could open up a 3 player replay, press e as soon as possible, open up a script i make called 3player.lua, 3player.lua connects you to a custom server. The custom server would relay joint positions to and from you you, the lua would work out the info sent from the server, set the joint positions and then advance you x frames, it could also display chat n such...
Buuuut as i said, that would take quite long to make, and the whole "open up a 3 player replay and press e as soon as posible" means that there is no set start frame for those who join, making it incredibly glitchy.