In the holodeck, I sometimes forget to move the mouse pointer to the corner of the screen before I unplug the keyboard. Here's how to do it remotely if you use fvwm (or fvwm2) as your window manager:
$ ssh whatever
$ export DISPLAY=:0.0
$ FvwmCommand 'CursorMove -100 -100'
Note that the quotes are important; otherwise it gets confused about the -.