Kil or communicate with process started by call-system

On XP, I'm using call-system to set up an SSH tunnel using Plink. I'd 
like to be able to either have the tunnel without keeping a command 
window open or minimizing the command window to the system tray and 
sending it an exit command when I'm finished with the tunnel.

Is there a way to do that? It looks like there is no handle to the 
command window created by call-system so maybe this isn't possible.

Mitch