Question - How to X Session on a local computer via remote computer

[Linux]

I am working simulation involving multiple computers to execute. Trying 
to "control" the simulation from one computer. From the controlling 
computer, I would like to start a user x-session without having to 
physically log on to that computer. The purpose is to bring up different 
graphical displays on all the computers. I can do it as root.

For a two computer example:
Computer Names: cpu1 & cpu2

Main user logged onto cpu1
Simulation is started on cpu1
Process for simulation is started via ssh on cpu2 -
cpu2 process starts a gui to monitor simulation progress on cpu2


If I am root, then I can leave the cpu2 at the terminal (console) login 
versus a graphical login (gdm/kdm). I can ssh onto cpu2 and issue a 
startx command. The gui (gnome or kde) on cpu2 will start.

But I can't do this with a user account because the user does not own 
console when it is at the login prompt.

Granted I can host the display on cpu1 but we are using around 10 to 15 
computers and I don't want all their displays going to one machine. 
Plus, when you are doing a dog & pony shows, it is a lot easier display 
data on multiple screens.

Ideally, I would like a limited user, simuser, that has the ability to 
run the simulation with just enough access to execute the simulation and 
to copy the output data. The simuser would get authenticated on the main 
cpu and then start the process via secure shells (although without a 
password) on the other machines. The other machines would bring up their 
displays as simuser. Once execution is done, the displays close out and 
the machines are back to a login prompt or window. The gui would be 
configured such that simuser could not create a terminal. And any 
attempt to exit the simulation would just take them back to the login 
prompt. Also when the simuser is not using the computers, they must be 
available for normal use.