I've created a tiny little application in python, with it you can control mplayer on your Kindle wirelessly from your computer over an SSH connection. I've included a readme file with instructions to get everything working. You'll need Jailbrake, usbNetwork and MPlayer (Launchpad is optional, but recommended).
I've tested it on Ubuntu 11.04. If you use Ubuntu, you don't need any special dependencies, everything is there (Python and GTK3), just extract the application somewhere, execute controller.py and it should work (you can also invoke a python control.py
command over it from a terminal).
Here is a screenshot of the application:
Hope you find it useful